9 replies to this topic

[Reece]

I am not sure if this makes any sense whatsoever. I wanted to ask more experienced members here for their thoughts.

 

Cooled astrophotography cameras cannot be worked into my budget unfortunately so the only option is DSLR or uncooled planetary camera.

 

Please forgive this newcomer for any mistakes below. 

 

The ZWO ASI120MM has:

 

1. Pixel size of 3.75um -- not much smaller than a Sony a6000, Nikon d7200, or Canon 80D that other members use.

2. Q.E. of 80% -- far higher than my present cameras (Canon 40D and Nikon J1). This would help make the best use of the light gathered. 

3. Read noise that is higher than other ZWO cameras. Could lights+darks+flats+bias frames allow cost savings here? 

4. Monochrome sensor - useful with certain filters. May also help image quality if LRGB imaging.

5. The potential to be a good camera for guided subs when I progress to that point

 

Because of the small camera lenses it would be used with, there would be a lot of wasted light and resolution with a larger sensor (such as my Canon 40D) that would not contribute to image quality on many DSO targets. The 1.2 megapixels of the ASI120MM are spread out over an area that is 4.8mm x 3.6mm in size compared to 22.2 x 14.8mm in a Canon APS-C camera such as the Canon 40D.  This is a 19x smaller area so the ASI120MM would put a comparable amount of pixels on target as the 24MP Canon 80D assuming the target fits entirely on the ASI120MM sensor.  

 

Given sufficiently long exposure time to compensate for the small noisy sensor, could this actually work?

 

Thank you so much for your help!

Edited by Reece, 20 January 2021 - 04:12 PM.

[fewayne]

If you have some means of putting filters in front of it that won't break the bank, sure. As with any uncooled camera, of course, you'll have to either shoot darks every session or build up a temperature-sorted library. I bought a 120MC-S for pretty much the same reason, figuring I could either guide with it or use it as a small-sensor one-shot color cam. Even with the Bayer filter matrix, it does pretty well as a guide camera, so you may wish to consider that instead of the mono model and the expense and trouble of filters. (Yes, see, sometimes I actually do recommend OSC over mono!)

 

You do want the -S variant of that camera, though. It provides USB 3.0, but is also connects more reliably, the non-S cameras are infamous for being glitchy. Not to say that no one has made them work, just that they're prone to problems.

 

Usually we talk about pixel size and image size in terms of the image scale, the number of seconds of arc subtended by each pixel. There's a nice calculator at astronomy.tools that explains the concepts and also lets you plug in various cameras and focal lengths to see if they're suitable.

[Stelios]

If you don't have a DSLR, you *could* use the ASI120MM, but you would need filters. 

 

The small sensor of the ASI120MM would be a tremendous limitation. You don't say what scope or mount you have, so it's difficult to evaluate your situation.

 

In general, if I had an ASI120MM and a DSLR, I would image exclusively with the DSLR. 

 

No matter what you use, get used to taking bias (only need taking once), darks (need to match temp and exposure) and flats (should be taken every time). It's a ritual every astrophotographer has to go through, like warming up before a sprint or weight-lifting session.

[Reece]

Hi Stelios,

 

I have a Canon EF 200mm F2.8 lens and a Canon EF 75-300mm F5.6 lens for a Canon 40D DSLR. I have not yet purchased a mount.

 

--

 

fewayne, thank you for bringing these facts about ASI120MM to my awareness. I did not know them.

Edited by Reece, 20 January 2021 - 05:04 PM.

[alphatripleplus]

If you want to try a small mono  camera, the ASI290MM has a more sensitive (and lower read noise) sensor than the 120MM.

[Borodog]

Yes. it will work. I've done essentially the same thing but with cheaper, crappier lenses. I used a color SV305, but still a small sensor planetary camera. At 200-300 mm you will have to carefully select targets that will fit in your field of view, and you will get very low resolution images of them. Your field of view would be roughly 1.3x1 degree. Use astronomy.tools to check out your FOV for various targets. M31 will not fit. The Orion Nebula will, but without the Running Man. Etc.

[TelescopeGreg]

Given a choice between an uncooled planetary camera or an uncooled DSLR, pick the DSLR.  Massively bigger sensor, and all the support for live viewing, storage, etc. all in a nice compact package.  And it takes "regular" pictures, too.

 

Don't discount the acreage required for DSO imaging.  Most targets are really large, and won't fit the smaller sensors.  And the smaller targets that do fit will be hard to find unless you have a really well aligned mount.  These are from experience, fighting with my first camera, a Skyris 236C.  Moving up from that to a DSLR was an amazing feeling, right up there with taking ones' boots off after a day of downhill skiing.

[HaraldMartin]

Potential arguments for the 120MM vs. DSLR (unmodded):

 

• Higher sensitivity to H-alpha
• Higher sensitivity of mono vs. color camera (i.e., no Bayer filter)
• Better suited for using narrowband filters
• Can use cheap achromatic lenses (instead of expensive APO) with little CA when focusing for individual color filters.
• Can use cheap old camera lenses (e.g., Minolta MC/MD) at low focal length (e.g., 28mm) for true wide field images.
• When using cheap camera lenses, the small sensor size may be an advantage because only the sharp central portion of the lens is used due to the small sensor size.
• Less weight, can get away with smaller mount.
• Images are captured on computer allowing plate solving to find targets. Thus, small FOV not a problem. Of course this would also be possible with DSLR that have a USB interface, like the Canons and Nikons.

 

Just some thoughts. Not sure if they all make sense, though.

 

Regards,

 

Harald

[robbieg147]

Hi Stelios,

 

I have a Canon EF 200mm F2.8 lens and a Canon EF 75-300mm F5.6 lens for a Canon 40D DSLR. I have not yet purchased a mount.

 

--

 

fewayne, thank you for bringing these facts about ASI120MM to my awareness. I did not know them.

 

That Canon 200 F2.8 is a gem of a lens, used with your 40D you will be able to get some great images.

[Al_N]

I had a bit of success with an uncooled ASI178mm, Ha filter, and either a Canon 85mm f/1.8 or a Takumar 135mm f/2.5 lens.

 

This camera has 2.4um pixels, and fierce amp glow. With sufficient dithering, full set of calibration files, you can get reasonably good detail of emission nebulae.

 

This thread contains one of my pics: https://www.cloudyni...age-135mm-lens/

 

I bought both color and mono cooled cameras this winter, so the 178m is my guide camera now.

 

CS

Al