How does a full-frame compare to a crop factor DSLR?

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jrkirkham United States of America
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How does a full-frame compare to a crop factor DSLR?

#1

Post by jrkirkham »


Here is a question that I've been thinking about. Does anyone on here have any thoughts on the matter?


I normally shoot with an ED 80 triplet and a Canon 80D. I use an Orion Sirius mount. I'm not a great photographer, but I have fun. I can usually count on getting 30sec. subs at ISO1600. I like this match because the camera is light and has an articulated screen that helps a lot at night. I can get longer subs on some nights, but 30 secs. is the amount that I can count on night after night.

I've been thinking, however, of using my Canon 6D. The 6D is heavier and does not have the movable touchscreen. It does have the ability to shoot at ISO3200 without much noise and since full frames have a wider angle screen I predict that I could get 45 sec. subs regularly. The target would need to be cropped more.

Does that sound accurate? Do you think the 6D would be a better fit? What are the advantages and disadvantages between full frame and crop factor DSLRs?
Rob
Telescopes: 50mm refractor, ED80 triplet, 90mm makcass, 10" dob, 8"SCT, 11"SCT
Mounts: Celestron CGX, Orion Sirius + several camera tripods
Cameras: Canon 6D, Canon 80D, ZWO-ASI120MC
Binoculars: 10x50, 12x60, 15x70, 25-125x80
Observatory: SkyShed POD XL3 + 8x12 warm room
AL Projects Completed: Lunar #645, Outreach #0280, Universe Sampler #93-T, Binocular Messier #871, Messier #2521, Messier Honorary #2521, Constellation Hunter Northern Skies #112, Planetary Transit Venus #1, Galileo #26, Outreach Stellar 0280, Meteor Regular #157, Solar System Telescopic #209-I, Observer Award #1
AL Projects Currently in Process: Double Stars, Comet, Lunar Evolution
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JayTee United States of America
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Re: How does a full-frame compare to a crop factor DSLR?

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Post by JayTee »


Hi Art,

Here is an article you may find interesting. It may not answer your questions (in fact, it could generate more), but at least you'll be fully armed with info.

In a nutshell, the 80D - smaller pixels means better resolution. The 6D - larger sensor means larger field of view. The 6D - faster ISO means same length exposure will produce a "brighter" image (this notion is heavily caveated though). The 80D has a newer Digic 6 processor - this is not really called into play for AP images though, but it could mean lower noise even at higher ISOs. The 6D heavier - you've already touched on this.

Here is a comparison from my favorite FOV website, notice the substantial difference in the FOV:
80D v 6D Comp.png
I don't know if this was much help,
JT
∞ Primary Scopes: #1: Celestron CPC1100 #2: 8" f/7.5 Dob #3: CR150HD f/8 6" frac
∞ AP Scopes: #1: TPO 6" f/9 RC #2: ES 102 f/7 APO #3: ES 80mm f/6 APO
∞ G&G Scopes: #1: Meade 102mm f/7.8 #2: Bresser 102mm f/4.5
∞ Guide Scopes: 70 & 80mm fracs -- The El Cheapo Bros.
∞ Mounts: iOptron CEM70AG, SW EQ6, Celestron AVX, SLT & GT (Alt-Az), Meade DS2000
∞ Cameras: #1: ZWO ASI294MC Pro #2: 662MC #3: 120MC, Canon T3i, Orion SSAG, WYZE Cam3
∞ Binos: 10X50,11X70,15X70, 25X100
∞ EPs: ES 2": 21mm 100° & 30mm 82° Pentax XW: 7, 10, 14, & 20mm 70°

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jrkirkham United States of America
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Re: How does a full-frame compare to a crop factor DSLR?

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Post by jrkirkham »


Thanks it was helpful, but I didn't see the link to the article. There are two things I was wrestling with. The difference between ISO1600 and ISO3200 is a full stop of light. That is double the light gathering ability. The larger sensor means a wider field of view, but does that also translate to a little more wiggle room before stars begin to trail. It seems like it should. As an extreme example, if I shoot stars with my 14mm lens as opposed to my 400mm lens the 500 rules suggests that I have a lot more wiggle room before stars begin to trail. I know that is not exactly the same with my mount, but assuming that I am not that good of a photographer, it may be similar. It is a lot easier for a beginner to track with an ED80 that an 11" SCT. If the 80D is a 1.6x crop factor and I know I can get consistent shots at 30sec. could I get consistent shots with the 6D at 45sec.? If so it seems like 45 sec. subs @ ISO3200 would gather substantially more light than 30 sec. subs @ ISO1600. However I am hearing a few drawbacks, such as less sharpness and perhaps more vignetting?
Rob
Telescopes: 50mm refractor, ED80 triplet, 90mm makcass, 10" dob, 8"SCT, 11"SCT
Mounts: Celestron CGX, Orion Sirius + several camera tripods
Cameras: Canon 6D, Canon 80D, ZWO-ASI120MC
Binoculars: 10x50, 12x60, 15x70, 25-125x80
Observatory: SkyShed POD XL3 + 8x12 warm room
AL Projects Completed: Lunar #645, Outreach #0280, Universe Sampler #93-T, Binocular Messier #871, Messier #2521, Messier Honorary #2521, Constellation Hunter Northern Skies #112, Planetary Transit Venus #1, Galileo #26, Outreach Stellar 0280, Meteor Regular #157, Solar System Telescopic #209-I, Observer Award #1
AL Projects Currently in Process: Double Stars, Comet, Lunar Evolution
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Re: How does a full-frame compare to a crop factor DSLR?

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Post by JayTee »


I hate it when I do that. Here's the link:https://www.the-digital-picture.com/New ... News=20575
jrkirkham wrote: Mon Jul 01, 2019 1:18 pmThere are two things I was wrestling with. The difference between ISO1600 and ISO3200 is a full stop of light. That is double the light gathering ability. The larger sensor means a wider field of view, but does that also translate to a little more wiggle room before stars begin to trail. It seems like it should. As an extreme example, if I shoot stars with my 14mm lens as opposed to my 400mm lens the 500 rules suggests that I have a lot more wiggle room before stars begin to trail. I know that is not exactly the same with my mount, but assuming that I am not that good of a photographer, it may be similar. It is a lot easier for a beginner to track with an ED80 that an 11" SCT. If the 80D is a 1.6x crop factor and I know I can get consistent shots at 30sec. could I get consistent shots with the 6D at 45sec.? If so it seems like 45 sec. subs @ ISO3200 would gather substantially more light than 30 sec. subs @ ISO1600. However, I am hearing a few drawbacks, such as less sharpness and perhaps more vignetting?
Okay, insofar as ISO is concerned. The ISO setting does not determine how many photons you are capturing. All it does is amplify the signal. And when you amplify the signal you also amplify the noise. Some DSLR processors are better at amplifying just the signal than others. The 6D having the older processor may not be as good at handling this amplification and so you will get increased noise.

Staying with the same telescope, the larger sensor does mean that your imaging scale will be different -- which in this case means larger. Having a larger imaging scale means that you do have more "wiggle" room before guiding/tracking errors become evident. With a crop factor DSLR, the 500 rule is realistically the 300 rule. If you do start to use the 6D (with its full frame), you can go back to the 500 rule.

Once again, remember that the longer your exposure, the more photons you have captured which has nothing to do with ISO. So the increased exposure time and ISO will give you a noticeably brighter image. It also means brighter LP noise too. Once again this noise has to be dealt with in post-processing.

By less sharpness, I assume you are referring to less resolution. This is true, you will lose some resolution, not because of the sensor size but because the size of the pixel on the 6D sensor is nearly twice as big as the 80D pixel. There are pluses and minuses to this. The larger pixel does mean lower resolution, but it also means that it can handle more photons before it gets "full". This typically means that you will have better star color rendition in your final image. And yes, the larger sensor will suffer from vignetting more so than will the cropped sensor. But this can all be handled in post-processing.

If your imaging setup can handle the extra weight of the 6D, I say give it a try. Since you already own it, it doesn't cost you anything to do this.

Cheers,
JT
∞ Primary Scopes: #1: Celestron CPC1100 #2: 8" f/7.5 Dob #3: CR150HD f/8 6" frac
∞ AP Scopes: #1: TPO 6" f/9 RC #2: ES 102 f/7 APO #3: ES 80mm f/6 APO
∞ G&G Scopes: #1: Meade 102mm f/7.8 #2: Bresser 102mm f/4.5
∞ Guide Scopes: 70 & 80mm fracs -- The El Cheapo Bros.
∞ Mounts: iOptron CEM70AG, SW EQ6, Celestron AVX, SLT & GT (Alt-Az), Meade DS2000
∞ Cameras: #1: ZWO ASI294MC Pro #2: 662MC #3: 120MC, Canon T3i, Orion SSAG, WYZE Cam3
∞ Binos: 10X50,11X70,15X70, 25X100
∞ EPs: ES 2": 21mm 100° & 30mm 82° Pentax XW: 7, 10, 14, & 20mm 70°

Searching the skies since 1966. "I never met a scope I didn't want to keep."

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jrkirkham United States of America
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Re: How does a full-frame compare to a crop factor DSLR?

#5

Post by jrkirkham »


Thanks everyone. You are helping me learn a lot. Now I guess I need to carve out some time to experiment.
Rob
Telescopes: 50mm refractor, ED80 triplet, 90mm makcass, 10" dob, 8"SCT, 11"SCT
Mounts: Celestron CGX, Orion Sirius + several camera tripods
Cameras: Canon 6D, Canon 80D, ZWO-ASI120MC
Binoculars: 10x50, 12x60, 15x70, 25-125x80
Observatory: SkyShed POD XL3 + 8x12 warm room
AL Projects Completed: Lunar #645, Outreach #0280, Universe Sampler #93-T, Binocular Messier #871, Messier #2521, Messier Honorary #2521, Constellation Hunter Northern Skies #112, Planetary Transit Venus #1, Galileo #26, Outreach Stellar 0280, Meteor Regular #157, Solar System Telescopic #209-I, Observer Award #1
AL Projects Currently in Process: Double Stars, Comet, Lunar Evolution
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Re: How does a full-frame compare to a crop factor DSLR?

#6

Post by dghent »


Have you considered a dedicated astro camera and filter set instead of a full-frame DSLR? For the money, going from a crop DSLR to a full-frame one just gets you one thing: a slightly larger FOV. It'll certainly be just that if the camera goes unmodded. That's kind of underwhelming for the price.

However for the price of a Canon 6D2 with kit lens, you can get a ZWO ASI1600 with 8-slot filter wheel (or the equivalent from QHY) for around the same price. Add in a cheap but effective LRGB+Ha/OIII filter set from Astronomik or Baader and you have yourself something made for and very effective at DSO photography.

It's my opinion that DSLRs are great for starting out. Entry-tier models can be had for $100-$200 used, and can also be used for terrestrial photography. But that's it. They're kind of a hack for astrophotography and don't offer any compelling features that actually facilitate it. So if you're looking to further develop your capabilities and skill in astrophotography beyond your first DSLR, the next step should not be another DSLR. It should be something that's actually made for the job and far easier to manage.
Scopes: Astro-Physics 130GTX (w/ FocusBoss), CFF 92mm f/6, Telescop-Service 130mm f/7, Orion XT10i dob (Protostar flocking, Moonlite focuser retrofitted)
Mounts: Astro-Physics Mach1GTO, Rainbow Astro RST-135, Fornax LighTrack II
Solar: DayStar Quantum, Quarks: H-alpha Chrom+Prom, Ca-H, Mg I-B2, Baader Herschel Wedge
Cameras: QHY294C, ZWO ASI1600MM, ASI174MM, ASI290MC, ASI290MM-Mini
Software: N.I.N.A., SharpCap Pro, TheSkyX, AS3!, PixInsight, ASTAP
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