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Altair GPCAM

JohnSadlerAstro

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Davesellars

Davesellars

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I have the mono version of it and used for DSOs.  It is very sensitive but it's also quite noisy.  You'll be quite restricted to only imaging small objects as it's only got a small sensor.   It is an excellent guide cam.   I would however  advise if you're budget limited to instead go for a second hand DSLR instead.  MPB photographic (i've used and been very please) and Wex Photographic have very good prices - you'll be able to pick up a 450D for example around £100.  Alternatively buy a second hand one from the likes of Cheap Astrophotography that is already modified.

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ChrisLX200

ChrisLX200

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IT should work OK for the brighter DSOs, but obviously not large targets (like M42 would be) with its 1/3" sensor. It's not a cooled imager so there is background noise (but neither is a DSLR and that has noise aplenty too...). You can use dark frames to remove most of the noise, and Altair Capture provides a nice dark frame library function which helps to do this. I have not fully explored the limits of the GPCAMs, but I do have both the colour and the mono cameras to play with. I use the mono one mainly as an electronic finder by attaching a 6mm lens to it, but the longest exposure I've used is 30sec. The colour version I will be using as a planetary imaging camera.

ChrisH

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Davesellars

Davesellars

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It's not available yet however the cooler developed is a passive cooler:  the information for it is here: http://www.altairastro.com/Altair-GPCAM-USB-Cooler-Module.html

The information I received from querying the performance and what the cooler actually was from Altair Astro on their Google Group was:

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If you switch on the fan in about 2 mins the reverse surface is noticeably cool to touch, we've  estimated 3.5 degrees delta at room temp with a cheap digital gauge. This isn't super scientific but the fan and increased surface area really do a better job of heat dissipation than the casing on its own.

These sensors run hot by which I mean you can feel the warmth of the casing by touch on a cold night as soon as exposures go above say 30 secs.

If you ever wondered why GPCAM never gets dew forming on the lens this is why -  because the casing has been designed to transmit heat away from the sensor.

Thing is once we've got that heat away from the sensor we need to dump it some way. Convection is a good method and better if we force the air too.

Now a telescope focuser can make a pretty good heatsink but the contact isn't as good with the casing hence the cooler - and of course for use with lenses.

Weve seen many competing cmos cameras have a similar apprach (though perhaps not as cheap or innovative) but it all boils down to two things, increase surface area and force air against that surface if possible.

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Now, I wonder how much difference this is actually going since it is passive to make in use for long(ish) exposures say 2 to 3 minutes?  I wonder as well if it would be possible to add in a peltier module somewhere?

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D4N

D4N

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Well the main challenge with adding a peltier is to ensure that it cools the sensor, if as they say the casing is designed to be a heat sink for the sensor then just attaching the peltier to the casing could work.

/Dan

Sent from my iPad using Tapatalk

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Davesellars

Davesellars

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Hmm, interesting.  At the moment the fan is attached to the heat sink of which I assume is just blowing air at high velocity directly at the heat sink to cool it down  Altair report that the heat sink will work better as the design of the camera originally was to use the focuser as the heat sink but as there is not enough of the body actually touching the focuser it is not efficient.

I remember reading that the design is such that sensor is essentially connected to draw heat away from it the the body as the Altair mention the sensor runs hot and the body warms up in use.   The reverse would be true if enough cold could be applied to the body not only to draw away heat but actuall chill the body and cool the sensor to below ambient temperature.  So, using the neat wrap around heat sink that Altair have designed pop on a peltier module on top of this add another heat sink on the hot side of the peltier with a fan blowing air in to cool the heat sink.    Would this seem like a practical solution?  ;) 

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D4N

D4N

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Yeh that's what I would do, it might be more difficult if you want to achieve set point cooling but if your happy just to cool the thing down that outa do it.

/Dan

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Davesellars

Davesellars

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For colour: at minimum, you'd need a manual filter wheel and then either LRGB and / or Ha + OIII (for nebulae)  Obviously, this costs a lot more that the camera so I would only recommend this route if later on you will upgrade the camera to a proper cooled CCD with a larger sensor otherwise go for a modified DSLR.   I don't really see any point in going for the colour version of this camera if interested in DSO imaging.

I did a bit of a session with this camera on Saturday night as my DSLR is with Astonomiser to de-filter it.  I used the Astronomik L (UV/IR cut) filter as is necessary and imaged M81 and M82 managing 3 minute un-guided subs.  Before, I've always used some other filter in the chain either the Skywatcher LP filter or my Astronomik UHC filter but this time I did not bother as I was imaging bright galaxies anyway...  I found in this case a decent halo around each star possibly reflection? But, also with such a long sub without a further filter it was bloating the stars horribly.  My focus was a little out perhaps but even so.   A UHC filter in the chain certainly seemed to control things better...  I'll see if I can upload both examples once I'm home!

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JohnSadlerAstro

JohnSadlerAstro

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Just a suggestion for getting good focus (though It's not perfect) is focusing the camera on the moon and then drawing a line around the focuser mount onto the focuser barrel. That way I found that I could just roll the focus in until the edge of the focuser mount hit the line I'd drawn, and I'd have quite good focus on my planetary cam's live view, which is difficult to achieve on dim planets like Saturn.

JOHN

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Davesellars

Davesellars

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John,  Here's M81 and M82 from Saturday night that I quickly processed in Photoshop. Both were 9 x 180s subs.  The Moon was playing havoc at the time so M81 needed rather more processing to bring it out a bit more so excuse the noise:  No darks applyed (can't get them to work properly with GPCAM images for some reason!)

post-38405-0-77483500-1445897244_thumb.j

post-38405-0-52181100-1445897246_thumb.j

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JohnSadlerAstro

JohnSadlerAstro

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Wow! I love the Galaxy images! :cool:  I once took a look at M81 & M82, but even though the night was a very good one, I could only just see them--it looks like the GPCAM really is good for Deep-Sky, like they say in the specs! Could the star bloating be anything to do with your equipment? I was wondering about getting a DSLR, but from my research it looked like that was going to be quite troublesome. 1st, my telescope probably won't have enough inwards focus to bring the camera into focus; 2nd the focuser itself isn't strong enough to take the weight of the DSLR.

Just a question, what mount are you using for your pictures?

JOHN

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Davesellars

Davesellars

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Hi John,

I'm using a Skywatcher NEQ6 - quite a hefty beast!  At the moment I'm imaging with my Skywatcher 80ED and this has excellent optics so I don't quite understand what is going on.  I don't believe the bloating is down to the scope as I don't see any issue at all using with the DSLR for long exposures.  It may well just have been down to bad transparency at the time / focus not quite dead on (I really need to invest or make a bahtinov mask!).   I have had better results with the stars with this cam before but normally I've taken shorter exposures or used with the UHC which seemed to control it much more for the longer exposure.

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Davesellars

Davesellars

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Have you thought about using a small refractor with ED optics (I assume you're using a reflector at the moment?).  Perhaps, look for one second hand they seem to come up frequently and also a second hand DSLR - it would cheaper than the GPCAM + filter wheel + filters for colour imaging.

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Davesellars

Davesellars

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Thinking again about what you said re-equipment possibly being the cause - It may well because I'm just popping the GPCAM in my diagonal that is causing these reflection halos?  As the Astronomik L IR/UV filter is always in place screwed into GPCAM directly (I believe this filter is reflective), there could be all sorts of reflections going on between the filter and diagonal mirror.  Next time, I'll omit the diagonal to see what difference it makes...

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