EEA with DSLR?

[Martyn87]

Pretty obvious one here I guess, but I'm putting together an AP rig at the moment based around a 6" SCT and was planning on using a DSLR with a large sensor to avoid having a really narrow field of view with this scope. However, as it's going to take a while to get all the gear together, I'd like to try out EEA. However, it seems most people are using either specific astro cameras or something designed for video use, like the adapted CCTV sensors, webcams etc. 

Is anyone using a DSLR for EEA? If so, any recommendations for particular models that work well? 

 

Thanks! 

Edited Thursday at 20:50 by Martyn87

[Elp]

It should work but you'd have to put some consideration into how short your subs are going to be (as you're imaging long focal length, I presume the mount will be equatorial) vs how large each image is as you need time for the data to transfer to the computer controller.

Pre made calibration files will also help the result, dark frames will be a must on a DSLR due to the internal temperatures.

[Martyn87]

4 minutes ago, Elp said:

It should work but you'd have to put some consideration into how short your subs are going to be (as you're imaging long focal length, I presume the mount will be equatorial) vs how large each image is as you need time for the data to transfer to the computer controller.

Pre made calibration files will also help the result, dark frames will be a must on a DSLR due to the internal temperatures.

Thanks Elp, mount is still a work in progress but is likely to be a (H)EQ5 or GEM28. Subs seem to be around 5/10 seconds but I guess I'll probably have to go longer with a DSLR? 

I really need to look at calibration. I understand the theory, but still not 100% sure on putting it into practice

[Elp]

Calibration don't necessarily need them to do EAA, but it helps the result you get when live stacking.

Flats you need to take images at the same temperature as your lights looking at an even and dimly lit light source (dimmable led tracer panels work well diffused with layers of t-shirt or paper), with a duration so your histogram peak is around a third from the left to up to halfway across the graph. If you're using a computer controller theres likely an in built auto flat routine which works it out automatically. Flats remove the vignette and any dust motes.

Darks you take at same temp and durations as your lights. These can be done by capping off the objective so no light gets through to the camera.

There are dark flats (as per darks, but same duration as your flats), bias won't work well with DSLRs.

Using a computer controller you tell the software where all the calibration images are and it should create masters of each, which are then used during your live session.

[Steve in Boulder]

How large a sensor does the DSLR have?  The Celestron C6 is the only six inch SCT I’m familiar with, and it is supposed to vignette pretty seriously with larger sensors.  The effect is worse if a reducer is used. 

[Martyn87]

Yep, it is a C6 (sort of anyways, it's a StarSense DX 6", but the OTA is basically the same thing). 

I'll likely end up with something like a EOS 100D unless I can get a mirrorless like an R100 for a good price. The sensor on the 100D is 22.3 x 14.9mm and I am using the F6.3 reducer. 

[Elp]

I'd stump for a 485/585/533 type sensor if you can. The former works well as a dso camera too, even though it's designed for planetary.

 

[Martyn87]

I had looked at the 585, but looking at the field of view tool on Astronomy Tools, I thought it was maybe a bit tight. The 533 looks a good option though, especially with it being square. 

Am I wrong in thinking that dark frames would help reduce the vignetting? I'm going to assume I'd be cropping too as I know SCTs have issues with star shapes towards the corners. 

[Elp]

Dark frames remove the dark current signal, flats remove the vignette and dust motes.

[Martyn87]

Thanks Elp. Looking again, the Altair 585C (https://www.altairastro.com/altair-hypercam-585c-colour-fan-cooled-usb3-astronomy-camera-13481-p.asp) actually looks like a really good deal, to the point it might convince me to forget about the concerns I have and go for one anyways. Especially as the C6 hyperstar doesn't support DSLRs so I'd have to buy an astro cam if I went down that route in the future. 

[Elp]

Note with Altair (I haven't seen anyone else do it they may do), they do fan cooled as per your link, and tec/peltier cooled which are the proper cooled astro cameras people normally buy which are more expensive. You can also look at player one, qhy, explore scientific I think do some, and SVbony as well as zwo.

With the Hyperstar I tend to use planetary cameras especially if doing OSC as exposures are usually quite short (10-30s), you just need to manage your cabling in a certain way to reduce the diffraction effect they can cause.

[Martyn87]

Yeah I've not seen anyone else do the fan cooled versions either, although Altairs TEC version is still around £100 cheaper than ZWOs, and player one don't seem to have a UK based retailer anymore (Starfield Optics are no longer trading). Plus, they're purple! 

In terms of the hyperstar, do you use it like this full time? If you were switching from hyperstar to using the rear port for a longer focal length, would you still go for the non-cooled version and shorter subs? 

 

Edited Thursday at 20:28 by Martyn87

[Elp]

I tend to use the HS the most, once you've experienced high speed imaging, slower is excruciating, I've also experienced this with my camera lenses are they're usually faster than most native scopes.

If imaging with the F6.3 reducer, I may still use an uncooled but the sub limit would be 90-120s, amp glow will start to become a factor for those sensors which don't have anti glow tech. The other issue is at higher resolution your signal is spread out over a larger sensor area, so a larger pixel camera may be better for such a scenario, or bin the pixels post capture. Using uncooled largely depends on ambient temperatures, in the UK it isn't so much of an issue.

 

[Martyn87]

Thanks Elp, I'm just thinking that the uncooled 585 costs around what I was expecting to pay for a half decent DSLR, so might be a more future proof option. I guess the shorter subs wouldn't be a big deal for EEA, and would potentially just mean I need to spend a little longer on each object? 

The way the weather is in the UK at the moment, this entire conversation is moot, haven't seen a single star for most of this week! 

[Steve in Boulder]

6 hours ago, Martyn87 said:

Yep, it is a C6 (sort of anyways, it's a StarSense DX 6", but the OTA is basically the same thing). 

I'll likely end up with something like a EOS 100D unless I can get a mirrorless like an R100 for a good price. The sensor on the 100D is 22.3 x 14.9mm and I am using the F6.3 reducer. 

I’ve used a ZWO ASI533MC  (11.3 x 11.3 mm) with the Celestron 0.63x reducer on my C6.   Some vignetting but fine with flats.  Things could be getting more critical with your selected sensor, so you may want to look into that.   Reducers will lower the acceptable image size.  

Edited Friday at 00:35 by Steve in Boulder

[Steve in Boulder]

4 hours ago, Martyn87 said:

Thanks Elp, I'm just thinking that the uncooled 585 costs around what I was expecting to pay for a half decent DSLR, so might be a more future proof option. I guess the shorter subs wouldn't be a big deal for EEA, and would potentially just mean I need to spend a little longer on each object? 

The way the weather is in the UK at the moment, this entire conversation is moot, haven't seen a single star for most of this week! 

Shorter subs as opposed to longer don’t make much of a difference for total signal-to-noise ratio.  The primary driver of that is simply total integration time.  With a fast setup and/or light pollution, shorter subs can even be beneficial.  

Hyperstar for the C6 is a relative bargain (relative to RASA or Hyperstar for larger apertures) and works very well for EAA of larger objects such as M31 and M42.  I like mine, but it is a little fiddly to collimate.   

[Elp]

7 hours ago, Steve in Boulder said:

it is a little fiddly to collimate.

I usually leave mine flat flush with no gap as instructed by Starizona.

[Steve in Boulder]

2 hours ago, Elp said:

I usually leave mine flat flush with no gap as instructed by Starizona.

That’s a good starting point, but wasn’t enough for me.