Large CMOS or CCD image sensors

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I'm considering replacing the eyepiece in a 6-inch newtonian reflector with an image sensor of some flavour... I've hacked up a web cam but the sensor at 1/4" is too small; the effective field of view is something under half a degree so I can't, for example, fit a whole moon in.

An adaptor for my DSLR won't allow close enough focus as the sensor is too far back in the camera body.

Anyone hacked a camera with a half-inch or larger sensor for this purpose? I need to be able to do long exposures (aka 'bulb mode') for deep space objects but also streamed images out to be able to stack them for noise reduction.

Or can recommend a hobby price (i.e. not a thousand quid!) sensor or camera unit? Or point me at data for the occasional sensors that pop up on the bay?

e.g. http://www.ebay.co.uk/itm/Sony-D...

My google-fu is not strong on this.

(though my captcha is, apparently)

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Hi Neil,

Nice to hear there are more astrophotographers on this site :)

I too have been looking at building my own camera, but to be honest, the price of sensors in low quantity I have found to be too close to a new camera with the same sensor anyway. Check out
modernastronomy.co.uk, the QHY series seems to be good value, I use the QHY5 coupled with the finder scope for guiding, it`s nice and cheap.

When I started imaging some 6-7years ago, I had the same problem as you. If you are really close to getting focus I would advice to disassemble the camera adapter(by loosening the three screws on the side of it) and attach it straight on to the focuser. You should get 8-10mm closer to the tube with that. Another 3-4mm can be gained by pushing the primary mirror up in in the tube using just the collimation screws. On my 4.5" I sawed off 25mm of the tube to achieve the same :P

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Quote:

Nice to hear there are more astrophotographers on this site

+1

Quote:
An adaptor for my DSLR won't allow close enough focus as the sensor is too far back in the camera body.

Hmmmm.. Strange.. Are you sure your focuser or adapter can not have a piece of the focuser-tube removed and the adapter then attached?

I (infrequently) use a Celestron 4.5 with

1) a photography adaptor crews onto the focuser-tube, and

2) an adaptor to convert the T-thread of the adaptor 1) to the bayonette of my SLR (in ancient days an Olympus OM-2, nowadays a Nikon DSLR).

The adaptor 1) consists of several parts that gan be set up in dofferent configurations depending on if I go for

- a wide-field "primary projection" (i.e. the camera sensor is at the primary focus), or

- a narrow field "ocular projection" (i.e. I drop an eyepiece into the adaptor 1) and the camera sensor is at the focal plane of the eyepiece). This has been of little use to me since I have no motor drive/follower for the Polaris mount. (*)

All the stuff is packed down a.t.m. so I have no opportunity right now to take photos.

IIRC when using the "primary focus" only a short piece of the adapter 1) is used.

-----

(1) Building a motor/tracker for my Polaris mount was the thing that got me started with AVRs all those years ago. I've been sidetracked ever since and still have no motor drive built. Most all the pieces (stepper motors, NJM motor drivers etc) are in nicely arranged storage..

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JohanEkdahl wrote:

Quote:
An adaptor for my DSLR won't allow close enough focus as the sensor is too far back in the camera body.

Hmmmm.. Strange.. Are you sure your focuser or adapter can not have a piece of the focuser-tube removed and the adapter then attached?

This is actually a common problem on newtonian telescopes, of the three I have only the last one worked for DSLR photography out of the box. The last one was designed with photography in mind, and it got a built in extendable focuser for use with eyepieces.
It is a byproduct of having the focuser mounted on the side of the scope really.

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Hmmmm. Waitaminute..

It might be that my focuser tube is in two pieces - the top one removed and the photo adapter put there instead. Hard to remember the details when you don't have the thing in front of you, and it's been a while since being used last.

IIRC, it was a moon eclipse perhaps 2008 or so. I got the new camera ring (T-thread to Nikon) shortly after I got the Nikon (two years ago?) and just got the photo adapter out to see that it all did fit together.

Also got an active 20 meter USB extension cable a while back and played around a bit with digiCamControl. The idea is to set up a series of shoots predefined. Then, only the pointing and focusing needs to be done "at the last moment". No more fixing with bracketed exposures by trying to manouvre the actual UI of the camera in the dark.

Just a predefined sequence 1/8, 1/4, 1/2, 1, 2, 4, 8, 16 seconds. Point, focus, press computer button. Click, click, click, cliick, cliiick, cliiiick, cliiiiick, cliiiiiick!

Re-point, check focus, press computer button, and off it goes again.

Extra advantage is that the images end up on the computer immediately. So the SD-card is for the usual "casual" daytime photographing. The astro-photos end up on the PC immediately. They will need editing, digital-darkroom work etc anyway. And 99 % of'em will be scrapped ASAP.

Now with a PC-controlled RA/DEC motor drive/tracker I could sit inside, by the fire, with the laptop, nice pot of tea, while the scope is in the garden. Luxury! :D

Inspiring subject, Neil. I need to get those steppers and driver-IC out..

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Re your problem, perhaps going for exchanging the focuser might be the smoothest option. Yes, it might cost several hundred (pounds), but then you will have the full quality of your DSLR available. I assume you are wise and it is a Nikon :wink:, but if not then digiCamControl does work for a selection of the (forcing myself to actually type...) Canons too IIRC.

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6-inch Newtonian, you say. Details? Make/model? Home-built?

As of January 15, 2018, Site fix-up work has begun! Now do your part and report any bugs or deficiencies here

No guarantees, but if we don't report problems they won't get much of  a chance to be fixed! Details/discussions at link given just above.

 

"Some questions have no answers."[C Baird] "There comes a point where the spoon-feeding has to stop and the independent thinking has to start." [C Lawson] "There are always ways to disagree, without being disagreeable."[E Weddington] "Words represent concepts. Use the wrong words, communicate the wrong concept." [J Morin] "Persistence only goes so far if you set yourself up for failure." [Kartman]

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Lol Johan, that is the first time I have heard Nikon being advised for astronomy(no, don`t want to open a can of worms).

Yes, PC-control is sweet when it works, and the ability to do guiding is really one of the biggest milestones there is in this hobby, I guess the next one is a permanent setup which I still strive for.

My current setup is a HEQ5 Pro mount, Skywatcher MN190 newtonian, Peltier cooled full spectrum modded Canon 350D as main imager and a QHY5 CCD for the guiding with the 50mm finder scope. All connected to an old laptop running XP. Add to that power and USB distribution on the the mount.

The control software is CartesDuCeil star map, EOS utility to download images, homemade software and hardware for camera control and PhD guiding for the tracking corrections.

Hope we don`t go too much off topic while waiting fro Neil to reply :P

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Thank you all for your insights, folks! Much to go on; the QHY stuff looks interesting.

1/ telescope is a cheap and cheerful Celestron six inch Newtonian reflector, on a Celestron own-brand alt-az tracking mount. When I get the date in the right format it's quite good at finding things in the sky and following them until I get bored (Actually, until Mrs Barnacle gets bored; it's her toy but I get to do all the going outside in the cold and setting it up).

2/ the DSLR is an Olympus E400 - so has no continuous video mode but does have long exposure modes. I have at present no remotes for it though that's not insurmountable

3/ The DLSR adaptor fails to make things short enough in the eyepiece by about a half inch as far as I can tell. Thank the moving mirror in the camera. There are no more bits to remove from the adaptor to make it shorter.

4/ I realise I can play with the mirror but I'm loathe to do that until I have explored other options; I certainly don't want to remove the possibility of using the existing eyepieces.

5/ I don't have anything that might go between the focus tube and the eyepiece.

6/ The proof-of-concept webcam viewer is simply an MS 3000 HD chopped in half and mounted in a bit of two inch plastic drainpipe. It's square and reasonably light tight, though I have not yet considered colour of flat field correction, so it basically works.

7/ Focussing is incredibly difficult, there's too much vibration from the focus being adjusted. The best I can get on a star is a blob, not a point, though I can get a point. I don't yet know if this is an exposure artifact or if perhaps there's an optical low-pass filter on the sensor (grr). Looking at Mizar, I resolve both stars with the larger about the size of the gap between the two...

8/ Tracking a star is very good once adjusted correctly; it holds the star in the same group of pixels for minutes at a time in my initial tests.

9/ I'm still playing with control modes in linux for the camera.

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Bear in mind: Even if your tracking of a certain coordinate is good, for long-time exposures you will need to "de-rotate the field" since you're on an Alt-Az mount. If you track a coordinate for 24 hourse (yeah-yeah, 23 hours 56 minutes and roughly 4.3 seconds) then the field in the camera will have rotated 360 degrees around that coordinate. So, for each minute of exposure you will get the camera field rotated 0.25 degrees.

RA-Dec mounts have their advantages. :D

As of January 15, 2018, Site fix-up work has begun! Now do your part and report any bugs or deficiencies here

No guarantees, but if we don't report problems they won't get much of  a chance to be fixed! Details/discussions at link given just above.

 

"Some questions have no answers."[C Baird] "There comes a point where the spoon-feeding has to stop and the independent thinking has to start." [C Lawson] "There are always ways to disagree, without being disagreeable."[E Weddington] "Words represent concepts. Use the wrong words, communicate the wrong concept." [J Morin] "Persistence only goes so far if you set yourself up for failure." [Kartman]

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Oh yes. I wanted a GEM mount but for now the AA mount is the only option.

But a grab'n'stack with some fractional rotation and probably shift should not be beyond the realm of programming, provided there are actually enough photons arriving in the cell to produce an electron at least every few samples.

On planetary stuff, of course, you have only a few minutes' exposure before the features rotate out of position; the moon is a nice easy stable target to practice with.

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For focusing on stars I recommend a Hartman Mask, there is generators on the web for printing them. It basically gives you a X and a horisontal line, when the horisontal line goes through the center of the X you got perfect focus :)

EDIT: A Bahtinov Mask was the one I was thinking of...

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That's something that could be of use, but it's not the immediate issue; I think rather that I'm blooming out the sensor at the moment. The focus does as it should but the best focus is still smeared over too many pixels.

The coarseness of the focussing rack is of course a mere courtesy detail...

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Ah, a couple of points to check then.

First make sure that the scope is collimated, e.g Make sure the mirrors line up perfectly, they should come with a simple plastic device that fits in the focuser and the procedure should be in the manual.

Try bringing down the exposures a bit. Bright stars like Mizar requires quite short exposures to avoid blooming. If that doesnt help you could try limiting the aperture, cardboard with a ring cut into it in front of the scope might help.

One idea could be to piggyback the Olympus on top of the telescope and image through ordinary lenses, just to get the feel for it. If the tracking mount is capable of alignment on a wedge then you are really up and running for wide field photography already :)

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Indeed, I'm playing with a number of options at the moment. One that I want to explore is a bag full of rice or beans (well, lead shot would be best, or tunsgten or depleted uranium shot!) to damp down vibrations in the telescope tube.

By eye, there is no problem with focussing stars to a point (surface features on Jupiter are visible) so I suspect the scope is close.

The scope in question is this beginner's device: http://www.celestron.com/astrono...

(ach, I knew I shouldn't have mentioned captchas)

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Looks way better than my beginner scope...

I know the stability problem all too well, my rig got about 11-12kg of equipment(30kg if you include counter weights and mount head) on it and it wobbles like a scared skeleton ghost if I look at it too hard.

The fact that you are able to see details on jupiter with an eyepiece and not with the webcam makes me think there is two(possibly more) problems. The obvious one is focus and exposure. On planets it is better to underexpose than overexpose, so dont be afraid of running it a bit low.

The other problem is atmospheric conditions. Our eyes is incredibly good at filtering the fast changing disturbances, but a camera just integrates it into a big mess.

The optimum way of imaging planets and the moon is shooting underexposed video, low exposure reduces the atmospheric disturbance, and the amount of images captured in a short video reduces the noise to compensate for the underexposure(and the atmosphere) ;) I have seen a few fantastic images taken with webcams, the philips toucam is a favorite in this segment(same chip as the early QHY5 i think).

With your equipment you should focus on planets and the moon(no pun intended) as a starter. Exposures longer than 10-15 seconds is rare with that mount unfortunately, so deep sky is very limited.

Experiment with the brightness settings and see if are able to reduce it so that no part of the image is bloated(could be done during daytime), then when you get a clear sky point to Jupiter or the moon and shoot a 60sec video. This you post process in Registax(free software) and see what you get.

I see you are located in the UK, check ukastroimaging.co.uk, they are a fantastic bunch of people an I`m sure you`ll get all the help you ever need there.

Cheers

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Thanks, that's pretty much the general plan.

Though it will probably be a while before I get too much chance to test again; not only are there the wonderful UK skies[1], so free of cloud and light pollution, to contend with, but in my copious free time I'm completing a Python course and am on final stages of publishing a book...

[1] sometimes as often as twice a year!

...and sometimes free of captcha, though not on this occasion.

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Had the bright idea of playing with the Olympus attachment in daylight. It turns out the furthest I can focus due to the light path inside the camera body is just past the end of the garden. Great for photographing spiders at long range, but not too hot for things effectively at infinity.

I suppose I can put some long bolts on the mirror, but I don't want to take it past the limits of the eyepiece. There's little scope (sorry!) for making the adaptor any thinner; it's only around 5mm at present.

** perhaps a mod would be so kind as to move this to the general topics thread? It's got a bit off for this one. **