DSLR camera questions

[casstony]

I've recently started taking a few pics with a dslr and I'm after a bit of advice.
I've been using a Canon 600D to take 30 second exposures at ISO 3200 through an Esprit 80. Should I be using different settings?

Also how much less noisy/more sensitive are the newer cameras like the 6D and A7S? Are they dramatically better?

I'm thinking of getting a Lacerta stand alone autoguider as I'm reluctant to add a laptop and CCD camera - prefer the dslr simplicity at the moment.

[Atmos]

Personally I think that you may be better off using 120s exposures at ISO1600. As for comparing sensors, I find http://www.sensorgen.info a good place to start. I found it relatively accurate with my Nikon D700 but you can always expect some variance camera to camera.

[doppler]

Without auto guiding 30 secs at iso 3200 seems to be the sweet spot for canon dslr crop sensor cameras. I keep the display turned off to keep the sensor a bit cooler.

[Camelopardalis]

The 6D is a fair bit less noisy than the 600D at the same temperature, but you'll still get noise speckle in your images on warm summer evenings, the 6D is just more tolerant of it. Just beware that a full frame sensor exceeds the imaging circle of the Esprit 80, so you might do just as well with a less expensive competing crop chip.

For your 600D...try dropping the ISO down to 800 and see how you go. The gain is quite high at 3200, with the unity gain being around 200. For the 6D it's closer to 800, so there's less amplification going on when using 1600 or 3200.

[casstony]

Thanks for the replies. I guess the first step is to get the guider and try the lower ISO's.
Colin, according to the list the 600D isn't too bad - not quite the dinosaur I though it might be.

Good point about the chip size and image circle Dunk. I also have larger refractors but the Esprit 80 is a nice setup - I'll have to look at prices of full frame vs APS-C and keep an eye on the classifieds.

I'm using an Advanced VX and had thought about a higher quality mount but the ease of use of the Celestron mount has me hooked. It takes me longer to physically set up the gear than it does to get the mount fully aligned including polar alignment.
I've got a GPS module and the StarSense accessory: StarSense aligns the mount automatically, then I do the All Star Polar Alignment routine, then another automatic alignment via StarSense - saves eyeballing and centering 8 or more stars.

[Camelopardalis]

I'd say save your money and get to grips with your 600D. There are less noisy sensors on the market now but it's constantly changing.

A mate of mine has the Lacerta and uses it with refractors large and small as well as SCTs and it works as well as a computerised setup as far as I can tell. It's not any cheaper than a computerised setup though. If you've got a laptop already all you'd need is a suitable guide cam and a guide scope, the learning curve is more or less the same IMO.

[jjjnettie]

The 6D is renown for it's low noise, but most of the Canons are pretty good when the ambient temp is below 10C. But come Spring/Summer, oh boy, the noise can be atrocious.
Darks frames are essential. At the end of each session I would pop a fresh battery in the camera and let it take darks until the battery runs out. Add those darks to your library and add more the next night and the next. Turn them all into one master dark frame to add to DSS.
Take them at all the ISO's you will use.

[casstony]

Thanks Jeanette. At least living in southern Victoria provides cooler night time temps for more of the year.

[casstony]

So I ordered the Lacerta MGEN autoguider today along with an adapter for a 50mm finder and a camera control cable.
Will I have to bother with PEC or will the guider take care of it all?

[Camelopardalis]

The guider should take care of it, at least for short exposures. The MGEN also supports dithering to help cancel out the DSLR pattern noise, etc. It's a pretty sophisticated box of tricks!

I've not imaged with my AVX beyond DSLR and a wide lens, but at f/5 you shouldn't need particularly long exposures. Aim for ISO800 or 1600 and see how you get on. It'll depend on how dark your sky is as much as anything else.

[Tony_]

The Lacerta MGEN is fantastic! I got one for my CGEM last year. I was thinking of getting a better mount but I got a better stand alone guider instead and now I don't really need a new mount. Easily control PE in RA and has some good features to control DEC backlash. Usually I disable the DEC guiding in one direction so it just corrects for drift. My stars are usually tight circles now and there is virtually 0 movement from the first image to the last.

Tony.

[casstony]

That's good to hear Tony. While looking around the 'net at comparisons the only negative comment I found related to it being a bit pricey, but everyone seems happy with how the MGEN works.

[casstony]

The MGEN guider arrived today and I used it tonight. Having never done any guiding before I had to read the quick start guide but it was fairly easy to use. It controlled the AVX well giving round stars in my esprit 80 with exposures up to 4 minutes. It seemed to be making adjustments constantly on either axis judging by the flashing LED's.

I also used the MGEN hand control to operate the 600D, setting it to take sequences of exposures of different lengths while I went inside and warmed up.
Nice little gadget and a good way to learn another increment in imaging without risking getting overwhelmed and discouraged.

Here's a 2 minute exposure at ISO 800 through the 600d using a 50mm finderscope for the guide camera.

[raymo]

Very nice indeed, be nice to see a dozen of those stacked.
raymo

[casstony]

That's next on the list of new things to learn. I've got half an hour or so of Lagoons from tonight to play with; been forgetting to take dark frames but, one step at a time :)

[Camelopardalis]

:thumbsup:

Darks are over-rated :lol: try the dithering function on the MGEN and forget about the darks.

[casstony]

Enabling dithering and no darks sounds like less work :thumbsup:

After stacking in DSS I end up with a really bright background, due mostly to light pollution I imagine? What's the easiest to use processing software?

[glend]

Can you post an example of this bright background result? I would disagree on not processing darks, they are important on DSLRs IMHO.

[casstony]

My Son has Photoshop on his school computer so I put a 20 minute stack into that and used the levels pipette thingy to get rid of the bright background, then stretched a little and it's not looking too bad.
The original looks much sharper but it's 182 MB; not sure how to resize but keep it looking better.

[Camelopardalis]

Yeah all you need to do to start with is adjust the black level so that the background looks darkish. I say "ish" because in this particular scene there are just stars everywhere, so not a true dark :lol: then adjust the white level so that they're not overblown (or "clipped").

[Camelopardalis]

Unless the DSLR is temperature regulated, it's a hiding to nowhere...it's not possible to calibrate the lights well when the sensor temperature fluctuates so widely over the course of a set.

Dithering, on the other hand, is much more effective (with a well behaved mount) at stacking out the pattern noise...this includes thermal noise as they won't occur at the same locations in the frame with respect to the subject.

Just MO :D

[casstony]

My AVX mount isn't well behaved by itself for imaging, but the MGEN made it track perfectly at 400mm focal length. I've got a variety of scopes to choose from all with very good optics - I'm curious to try imaging with the 8" Edge @ 1400mm to see if it holds up.

I took a set of darks last night anyway to see if it makes any difference - haven't re-processed yet.

The Lagoon images I took were with no moon and no filter. I'll try my IDAS LPS P2 next time to how much it helps.
I'm on the border between yellow and green zones.

[Camelopardalis]

Yeah the AVX should be interesting @1400mm. Both axes on mine are fairly stiff with the clutches off so you never know until you try ;)

I've done some imaging with my Edge 8 and reducer and the Celestron OAG. With all that the focal length works out at about 1450mm, but it guides easily enough on my EQ6. I've even taken some images with my full frame with that setup and it was barely vignetted (to the eye).

[casstony]

I restacked the Lagoon image with darks and compared the images. The first one had a couple dozen blue and red speckles through it (had to look close) which were removed in the second image via the darks.

Night time lows are currently around 3 degrees. Typical summer low temp's are around 15 degrees. How much worse should I expect the 600D noise to be in summer?

[Camelopardalis]

Noise doubles about every 6C increase in temperature, consequently you need a lot more subs to reduce it. If you're handy, knock up a little alloy box big enough to house it and stick a Peltier cooler on the side. There are several designs around, but check out Gary Honis' website for a good read.

If you're going to use it solely for astro it might be worth considering fitting a cold finger and removing the IR filter. The possibilities are endless! :lol:

[casstony]

I'm keeping things simple at the moment: using the family DSLR for astro, easy to set up and control AVX mount, simple stand alone autoguider.

For some reason though I find myself reading reviews of the SXD2, CEM60, Sony A7s, etc....... don't know what that's about.
Gotchas I've read about:
- Sony A7s removes small stars along with noise.
- Vixen SXD2 has no polar alignment routine

[Camelopardalis]

Built-in polar alignment routine isn't a golden egg. Drift alignment is the way to go, it's independent of mount "intelligence" ;)

I wouldn't expect to get 4-5 minute subs out of an All-Star alignment...

[casstony]

I like how fast the ASPA is and it did ok with 4 min exposures on my first guiding session (with 400mm focal length).
If it's easy to set up I tend to keep observing and if it's easy to set up and get PA I'll keep imaging. If it's a PITA to get ready I might just watch a movie instead :)

All advice welcome though and I take your point about drift alignment being better.

[Tony_]

Tony - I tend agree with you about set up time. I have to set up from scratch everytime. It takes me almost 1.5 hrs before I am taking my first image. I don't want to add to that. I find the aspa is okay and the MGEN corrects well even at a focal length of 2300mm. I can get 2 min subs unguided at f480mm

Tony.

[casstony]

Tony, I can be set up, polar aligned and guiding in half an hour, provided no gremlins pop up. My gear is stored near the observing spot and I have tiles on the ground to mark the position of the tripod feet.

I reckon the CGEM is due for an update anytime - hoping for a lighter mount with belt drives.

[Camelopardalis]

You've hit the nail on the head I think and so if you can get results with the ASPA then even better :thumbsup:

[casstony]

Got 10x3 minutes of eta before the clouds came in tonight. I was a little more careful with the ASPA and the stars are very round in the enlarged original file.
So the guided AVX seems quite adequate for shorter focal lengths.

[Camelopardalis]

Cool :thumbsup: I'll have to give it a try, it's a nice lightweight mount.

[casstony]

Looks like I'll score a clear night on Wednesday and I'm keen to get some more imaging in.

ISO 800 seems to work well with the 600D but should I use different ISO's for different objects? Would ISO 400 be better for clusters to bring out star colours? For longer focal lengths and galaxies is there a best ISO?

With a bit of moonlight would shorter exposures be better?

[Cimitar]

Hi Tony,

I'm also using a Canon 600D (un-modified), had it for approx 15 months. I'm using it with an 8" SCT and image at F10 + F6.3. I find ISO 800 is best for the camera and I can achieve 10min subs when my guiding is good. The sweet spots with this camera appear to be: 60sec = ISO 6400; 120sec = ISO 3200; 270sec = ISO 1600; 300-600sec = ISO 800.

If I'm imaging nebula, galaxies and galaxy clusters I aim for 10min subs at ISO 800. I tried 15min at ISO 800 however there was too much noise. If I have trouble guiding I drop to 270sec at ISO 1600 (not sure why but I've found 300sec at ISO 1600 produces more noise than 270sec).

Long story short, I created some test images using the figures above for each ISO and noticed that the end result (brightness wise) was the same for each image, except noise. The ISO 800 image at 10mins was the cleanest. Mind you, using a 10min sub each time will take a significant proportion of your night and may result in lost subs due to wind etc. Hence of late I'm generally sticking with 180-270sec subs at ISO 1600.

If the moons out you may need to reduce the exposure time and/or ISO as you'll get a washout effect and you may have trouble distinguishing your target from the background. For brighter objects like the Tarantula it's possible, however you may struggle when compared to say The Helix.

Cheers, Evan

[Camelopardalis]

Tony, a little moonlight is OK while testing, but unless you're on the opposite side of the sky even a little crescent can cause a background gradient.

ISO / gain is one of those things you'll need to experiment with to see what gives the best results on your targets. ISO1600 is another doubling of the signal and noise.

Remember the goal is to maximise signal over noise...if you inspect the histogram, aim to have the big peak about 20-25% away from the left edge, then that should mean your background sky is over the read noise.

[Atmos]

I find that this is largely accurate:
http://www.sensorgen.info/CanonEOS-600D.html

Following this I personally wouldn't bother going below ISO 800. The read noise does continue dropping but so does the dynamic range.

[casstony]

Thanks guys, much to consider. Given the 1/4 moon I might take the opportunity to test the AVX with the an 8" Edge and try a galaxy and higher ISO.

[casstony]

The test with the Edge didn't work out because I was too cavalier with setup, got over-confident, so I went back to basics.

In the couple hours between sunset and moonrise last night and with cloud bands rolling through I scrounged another successful image - I paid attention to good alignments and calibrations and tracking was perfect with the AVX and Esprit 80. Even with thin/moderate cloud rolling through the MGEN never lost its guide star.

The LEDs on the MGEN are constantly going on/off, showing the guiding corrections. Is that normal for guiding with any mount, or do the guiders work harder with lesser mounts?

[Camelopardalis]

I can only chime in with observations about using PHD2 with my EQ6...if I balance too well, it's pulsing back and then forth in RA ever couple of seconds. If I've done a good job of polar alignment then Dec corrections are rare - maybe a couple a minute.

Iffy seeing can cause too many corrections as the guider thinks the star is moving when it may just be bloating / fluctuating.

What sort of exposure time are you using for the guider? There will most likely be a sweet spot between ignoring the above chasing and seeing noise in the guider image...try 1 or 2 second exposures. There's a risk that too frequent pulses from the guide box coupled with backlash in the mount mechanism may amount to mischief.

My sense is that as a starting point you just want round stars across the field.

[glend]

I agree, i usually use a guide period of 2 sec, but that is with Metaguide.

[casstony]

My seeing is almost always unstable, so I'm mostly restricted to lower power viewing and I guess lower magnification imaging. Fortunately my yard is fairly dark.

The guiding exposure time is 1 sec. I had to look that up as I'd only read the quick start guide and the guider just worked - plug and play is good :thumbsup:.

I just enabled the dithering today so it'll be interesting to see how that goes - I've set the value at 10 pixels.

Next clear night I'll be trying my TSA120 with an ES 0.7x reducer.

[Camelopardalis]

Nice one Tony, look forward to hearing/seeing how you get on :thumbsup: