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Is Sony Really Alpha?

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#101 mpgxsvcd

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Posted 28 January 2015 - 08:22 PM

And the last one.

 

Total with only QE and DR.

Attached Thumbnails

  • Camera Comparison Just QE and DR.jpg

Edited by mpgxsvcd, 28 January 2015 - 10:38 PM.


#102 Relativist

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Posted 28 January 2015 - 08:57 PM

I know someone that uses the A7s at the highest ISO setting in video mode. He broadcasts on NSN every now and then. One question I had about it's functionality in video mode, in HD resolution, is it down-sampling, and if so does that help to increase the low light performance?



#103 orlyandico

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Posted 28 January 2015 - 10:00 PM

I thought the E-PM2 would be a great choice (and I can get one cheaply...)  and I think Jon's criteria (use the closest common full-well) is a good choice as well.  The pixels are quite small but surprisingly the full-well is decent.

 

However, I think that equivalent ISO (which is basically gain) and the pixel area should be figured in, and not just have a quality factor that is a % of each parameter - my Q1 parameter actually has a dimension and means something physically.

 

That said.. can the E-PM2 be tethered? Olympus web site only talks about the OM-D EM10 (or is it..)



#104 mpgxsvcd

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Posted 28 January 2015 - 10:37 PM

I thought the E-PM2 would be a great choice (and I can get one cheaply...)  and I think Jon's criteria (use the closest common full-well) is a good choice as well.  The pixels are quite small but surprisingly the full-well is decent.

 

However, I think that equivalent ISO (which is basically gain) and the pixel area should be figured in, and not just have a quality factor that is a % of each parameter - my Q1 parameter actually has a dimension and means something physically.

 

That said.. can the E-PM2 be tethered? Olympus web site only talks about the OM-D EM10 (or is it..)

 

The nice thing about the E-PM2 is that it doesn't need to be tethered. You can use a wireless intervalometer with it to sequence all of your exposures. It also has a very handy Bulb time mode that allows you to see the exposure gained so far during the entire exposure process. Basically it shows you what light it has collected every certain amount of seconds. That allows you to center even Dark D.S.Os without the need for a computer to control it.

 

It is really wonderful to be able to align, calibrate, center, and image without any wires or computers. When coupled with a fast aperture scope it can also do it in very short shutter durations if so desired. I typically use 1 minute ISO 6400 subs with my F4.0 scope when I just simply don't want to guide. I can always hook up the guider and go out to 8 minutes instead at much lower ISO values but it is always nice to have the choice.

I have never found anything that I wanted to do with the E-PM2 that I couldn't do directly in the camera. Some people will like that, others won't. You really have to see it in person to realize the benefit though. While everyone else is setting up their tables, cables, and computers I am already imaging.

 

The handy 14x crop sensor mode also allows me to accurately center my alignment stars and get my focus dead on. Also the 2x crop factor is excellent with 800mm scopes. It allows you to get M42, A full Moon, and the Rosette Nebula to fit in the frame yet it still can see fine detail in smaller objects like the ring nebula and the planets. It is such a wonderfully versatile camera.

 

I have a feeling that the Panasonic GH3 might actually be better for A.P. though. I have that camera but I didn't want to modify it because I use it for terrestrial images. It has built-in wireless and a really handy live view out to 8 seconds(ie: 8 seconds per frame). The E-PM2 works great though so I can't really complain.

 

Both cameras have essentially the same sensor. They both are excellent cameras for A.P. and in the E-PM2's case it is very inexpensive.


Edited by mpgxsvcd, 28 January 2015 - 10:42 PM.


#105 orlyandico

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Posted 28 January 2015 - 10:42 PM

Thanks!

 

Have you seen that guy who modded an M4/3 "from the front" by simply breaking the dust shaker?  it's something I want to look at...

 

http://www.mu-43.com...ead.php?t=44060


Edited by orlyandico, 28 January 2015 - 10:43 PM.


#106 mpgxsvcd

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Posted 28 January 2015 - 11:27 PM

Thanks!

 

Have you seen that guy who modded an M4/3 "from the front" by simply breaking the dust shaker?  it's something I want to look at...

 

http://www.mu-43.com...ead.php?t=44060

 

I wish I had never looked at that link. That is just messed up. Brent Oliver doesn't charge that much to modify them. That just looks destructive.



#107 orlyandico

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Posted 29 January 2015 - 12:02 AM

If I get an E-PM2 or E-PL6, I'll probably do that destructive mod... it's far easier than undoing all those ribbon cables, etc.  As I'm not in the US, the cost of shipping a camera back and forth for modification is inconvenient.

 

Anyway I modified my spreadsheet, as per Jon's suggestion I picked an ISO (and equivalent ISO) where the full-wells are comparable. Of course here the A7S gets far ahead.  I also changed Q1 to be the square root of (pixel_size ^ 2 * QE * equivalent_ISO).

 

Cameras-by-Q2.png


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#108 Jon Rista

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Posted 29 January 2015 - 12:09 AM

When it comes to the camera specs were pouring over in this thread, I think it helps to think about what it is were going to do with any one of these cameras. In the grand scheme of things, I think we do one of two things: Image at a chosen focal length, or image at a chosen image scale. Now, I've only been at this for not even a full year at this point, so (barring fringe activities like spectroscopy and things like that) if there are other options, feel free to correct me here. If this is true, that in general we either have picked a scope, and are either picking a camera or changing cameras...or we are picking an image scale (which may involve changing just the camera or both the camera and scope to achieve it).

In light of "This is what we do", I think the use of linear microns as a measure for pixels can sometimes obscure the real differences in pixels with larger pitch. This can be gleaned from Mike's charts...the A7s seems disproportionately good when you see it's pixel pitch of 8.3 vs. the 6D's 6.5...but if you swap out pixel pitch for pixel area, then the differences start making a lot more sense. Sometimes pixel size simply doesn't matter, either, depending on what your goals are...but if it does, then a linear pixel pitch isn't telling us the whole story. Maybe some clarification of what actually occurs when doing different things might help people make the right decision when it comes time to buy a camera.

There are three key factors that really matter, I think. First is pixel size. This is usually represented as a scalar, but it's really an area (the scalar squared.) The next important thing is rate at which that area is converting incident photons to free electrons (charge) in each pixel, or quantum efficiency. Finally there is the noise. With DSLRs, I'm not sure dark current is a problem during winter...and depending on the exact model, it may not even be a problem during summer (particularly talking newer cameras here). Read noise may be a factor...but, I've noticed a pattern that may nullify it (depends.)

Anyway, regarding pixel pitch. We look at the difference between "8.3µm" A7s pixels and think it isn't all that big of a difference from the "4.1µm" pixels of the 7D II. We see, just by looking at those numbers, what seems to be a factor of two difference (8.3/4.1 = 2.02x). In reality, the difference is larger than that. It's not the linear pixel pitch that matters, but the area: 8.3^2 = 68.98, vs. 4.1^2 = 16.81. The difference in light gathering capacity (ignoring quantum efficiency for the moment) is a factor of 4.1:1 in favor of the A7s, in terms of pixel area.

Factor in Q.E. now, or the rate of photon to electron conversion. If we assume we get 0.05p/m/µm^2, the A7s is converting 3.445 photons to 2.239825 electrons every minute each pixel. In contrast, the 7D II is converting 0.8405 photons to 0.495895 electrons every minute each pixel. The A7s actually has a 4.5167:1 advantage over the 7D II: 2.239825/0.495895. That is a four and a half stop difference...in absolute terms (just to put that in perspective...10m exposures with the 7D II @ ISO 1600 would become 20s exposures with the A7s @ ISO 6400!!! I truly don't think many cameras can do what the A7s could, at least in theory, do...now I really want to test it out in real life and see! :p) Same photon flux per given unit area (one square micron). That is not the same image scale...same focal length, say 1000mm.

If we assume the same image scale, that normalizes the photon flux per pixel, rather than per absolute area. If we assume 3p/m/px photon flux, then the only differences that really matter are RN and Q.E. The difference between the 7D II @ ISO 1600 and the A7s @ ISO 6400 are less than 0.1e-, so basically meaningless (especially once you start stacking...small changes in RN become less and less meaningful the more you stack). That makes Q.E. the deciding factor for same-image-scale imaging: 65% beats 59%, simple as that: 1.95e-/m/px vs. 1.77e-/m/px, assuming a real photon flux of 3p/m/px. The A7s has about a 10% advantage over the 7D II at the same image scale...but that also means your imaging at a much longer focal length. You would be imaging at a focal length 8.3/4.1 times longer, so if you used 1000mm with the 7D II for 0.84"/px, you would have to image at 2024mm with the A7s for 0.84"/px.

Differences in read noise and dark current affect how quickly we reach a point where our SNR is good enough (background sky swamps electronic noise). Less of either or both means we reach that SNR (per sub) faster. A pattern I've noticed, partly because I've pored over sensorgen's data for years, is that when we normalize the FWC, it seems pretty common that we also see a normalization in RN. Not a total equalization, but the differences in read noise become minimal, not even 1e- most of the time. (CAVEAT: If your looking for more dynamic range, then you might be forced to use a lower ISO setting...which often brings with it higher read noise. Then read noise might matter...but only MIGHT.) Dark current might matter, it might not. Older cameras are going to have higher dark current than newer cameras. Some new cameras have such low dark current that even at high temperatures (i.e. summer nights) the dark current isn't enough to be concerned about unless you are doing extremely long subs. So, anyway...on an FWC-normal basis, RN doesn't really change much, so it can probably effectively be ignored. My 5D III and 7D both definitely have problems with dark current at higher temperatures. I don't think a 7D II would at all, a 6D probably only during much warmer nights. It sounds like the NX1 is probably in the same class as the 7D II, so again, it wouldn't matter. A lot of cameras using Sony sensors are probably going to exhibit much better noise and dark current characteristics, even going back a few years, than older Canon cameras.

Oh, one other important factor that should probably be considered: resolution. Obviously there is a difference in resolution, and in that case the tables are turned, the 7D II resolves about four times as much detail as the A7s...however if you are sufficiently oversampling, any additional resolution of the 7D II is largely going to be wasted. The 7D II will pair better with short focal lengths. If your imaging at 400mm, both cameras will be undersampling, however the 7D II will undersample less severely than the A7s. The ultimate wide field camera might actually be the D810...that's an expensive puppy, though...and you might gain more advantages by going with a mono CCD + FW at those price levels. (Still, I see some PHENOMENAL results from the D810...just check out Wei-Hao's work on AstroBin, amazing stuff, has a distinct "CCD-esque" quality to it.)

So anyways...if your looking at a camera, think about what you'll be doing with it, and why. Are you just looking for a better camera to go with your existing scope? Are you looking to image more quickly with your given setup, or are you looking for a better image scale? Are you looking to image AT a certain image scale, and are willing to change both scope and camera to achieve it? Which camera would be ideal is going to change depending on how you answer these questions. The A7s is, without a doubt, a stellar performer (ignoring the "RAW" compression, although having used an A7r myself, I think the impact of compression artifacts are a little overblown...it requires some fairly specific data to produce the posterization, primarily hard edges against a fairly even-toned backgrop with the right amount of deviation in pixel value...like star trails)...but it may not meet everyone's needs. It has giant pixels. Those are certainly better for imaging at longer focal lengths, where you otherwise might end up with a 0.4"/px image scale with most cameras, and be oversampling to an obscene level. The big sensor can help you get really nice wide field shots...but those big pixel could potentially result in bloated stars. The 6D also has a big sensor, but it's got a better pixel size for wide field imaging (and again, the D810 is even better here.) It won't perform quite as well as an A7s, but it's still a stellar performer (sorry for the pun.) Most of the APS-C cameras, like the 7D II, the NX1, the D5xxx's and D3xxx's, are all sporting pixel pitches that are pretty ideal for some of the more common focal lengths up to around 1200mm or so, giving you decent image scales that nicely oversample at 2-3" seeing unless your going really wide (less than 600mm).

Oh, there is also the cost factor. I don't think about cost so much myself...not sure why, I guess I just figure I'll save till I have the funds then go for it, regardless of cost. :p I think about value for cost more, I guess. To me, I see $3400 for a D810, which is close in price to the $3000-$4000 price range of a lot of high quality mono CCD cameras that can use OAG and filter wheels and offer regulated cooling (just for the fact that it makes getting temp-matched darks a synch), and offers a 100% fill factor for every filter you use (vs. a 50% FF for green and 25% FF for red/blue pixels in a DSLR, even an astro modded one.) I'm sure budget is a factor for many, but within a given budget, the information above would still apply.

Edited by Jon Rista, 29 January 2015 - 12:19 AM.

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#109 orlyandico

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Posted 29 January 2015 - 12:30 AM

actually Jon, my "Q1" number totally encapsulates your essay.  You can see that the A7S has about 4X the Q1 of the 7D II.    :grin:

 

Now of course the information at a given focal length is different.

 

The reality is, for a given focal length and exposure time, the amount of information is fixed.  Hence if you use an A7S, sure you get more signal (better SNR) but you lose detail.  The 7D II would give more detail but more noise.  So the information in both cases is still fixed.

 

However read noise is a big factor here, because RN will put a baseline that you have to get above, before you are getting useful signal.  That's what the Q2 number reflects.

 

I'm having second thoughts about the DSLR.. probably thinking of getting an Atik 414 (ICX825, 73% QE!) but its read noise would be around 4e- which is triple these DSLR's.



#110 Jon Rista

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Posted 29 January 2015 - 12:59 AM

Ah, I see you updated your Q1 to square the pixel. Nice! :D I hadn't seen that when I was writing my post...I started writing it, then walked away, then came back and finished it...I guess a few posts were added in that time.

 

Anyway, yeah...I like your latest table. Good data. The read noise levels of the A7s and D5200 blow me away...1.6e-!! Isn't the D5200 the camera with the Toshiba sensor as well? Well, all I can say is, go Toshiba! :p

 

Too bad we don't have data on the NX1 yet. I have a friend from another forum who has one. I asked him if he could get me a series of data for bias frames, dark frames and step wedge (dynamic range) frames at each full-stop ISO setting, and at a few different temperatures (room temp, 10C and 0C). Not sure if he will be willing to spend the time or not...if he is, maybe I can produce some read noise, FWC and dark current data for the NX1 that we could use here. If this guy isn't willing to, maybe I'll just rent an NX1 myself and generate the data, then share it with Bill Claff (he's more adept at producing viable numbers than me anyway.) 


Edited by Jon Rista, 29 January 2015 - 01:00 AM.


#111 mmalik

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Posted 29 January 2015 - 01:30 AM

I hate 6D for one good reason (besides its size...), not having an articulated LCD, if you can understand that... I don't use a laptop and look at LCD for focusing, histograming, previewing, etc. I see a7/a7II a viable alternative to 6D (for that matter a7S); a7/a7II may be the best for both short/long FL scenarios (that Jon descries above... in terms of oversampling). I am looking forward to giving a7/a7II a try for testing sake at least. Price is also lesser or equivalent of 6D for a7 ($1,298) and a7II, respectively. 3" Tilting LCD (921,600/1,228,800) of a7/a7II will be a great replacement for a laptop. Regards


Edited by mmalik, 29 January 2015 - 05:51 AM.


#112 Jon Rista

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Posted 29 January 2015 - 01:45 AM

I can totally see articulated screens being very useful for those going non-laptop. Maybe even more importantly, for those going hyperstar or RASA, where the camera has to be on the front of the scope. With a high resolution articulating LCD, that should make it a lot easier to frame and focus when doing that kind of imaging, where it might otherwise take a step stair or something to get the right viewing angle on a fixed LCD.



#113 Jon Rista

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Posted 29 January 2015 - 01:54 AM

Oops, I made an error in my post above. I said the difference between the A7s and 7D II was 4.5 stops. That was wrong. The difference in light gathering capacity was 4.5 TIMES, which is 2 1/4 stops. That means the A7s can do in about 2 minutes what the 7D II can do in 10 minutes. Sorry about that...I was re-reading my post, and looking at that "20 seconds" and really wondering how I'd come up with that. 

 

Still...10 minutes vs. 2 minutes! That is still a HUGE difference. :p



#114 Cymrych79

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Posted 29 January 2015 - 03:35 AM

I believe the takeaway from these charts is that the Canon 550D is never a good choice if you are only considering these parameters even if cost is a factor. With this data it never finishes ahead of the Olympus E-PM2. However, I completely understand that other parameters that are not in this chart like BYEOS could sway someone to use the 550D. However, it clearly is not a good choice for image quality even when price is considered as well.

 

Been lurking here for a while, but I just wanted to pop in to say that nothing you're presenting in your charts has any bearing of the actual image quality from any of these cameras. You're effectively measuring the efficiency of the cameras, with a strong bias towards as rapid an acquisition as possible. And yes, the 550D certainly lags far behind every other camera in the list ... it definitely doesn't mean one can't take a quality photo with it however. It'll just take more subs and a longer total duration.

 

Don't get me wrong, I think your charts are pretty interesting. I always like to see data presented in new, unique ways! And for someone in really light polluted red skies, it makes total sense that you're looking for a camera rig that minimizes your exposure times while maximizing your photon count. I'm just saying don't count out the T2i for others who might be reading this thread who have other requirements that are more important, like cost, resolution or image scale, and don't mind sacrificing a little bit of extra time on their acquisitions. :)



#115 orlyandico

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Posted 29 January 2015 - 04:44 AM

well... time is money.   :lol:   the longer the exposure, the better the mount required.

 

i tried this route.. got an f/2.8 astrograph (newtonian with keller reducer).  Amazing light gathering capability.. impossible to collimate properly.   :undecided:   hence not a single round star anywhere.  Gave up on that.  f/4.6 (the same newtonian with a Paracorr) is much tamer and much easier to use... with 3X longer exposure times.



#116 mmalik

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Posted 29 January 2015 - 07:09 AM

The A7s is, without a doubt, a stellar performer (ignoring the "RAW" compression, although having used an A7r myself, I think the impact of compression artifacts are a little overblown...it requires some fairly specific data to produce the posterization, primarily hard edges against a fairly even-toned backgrop with the right amount of deviation in pixel value...like star trails)...but it may not meet everyone's needs.

 

a7R at 36MP does NOT seem suitable contender for astrophotography

 

 

a7S at 12MP is pricey; seems more suitable for longer FL

 

 

a7/a7II at 24MP are decently priced; a7II is more ergonomical with bigger grip. a7/a7II seem suitable for both long and short FL; a7/a7II seem closest match to 6D in pixel size/performance with much smaller & stylish body, and probably best for those wanting to give Exmor sensor a try...

 

 

Your thoughts?


Edited by mmalik, 29 January 2015 - 11:07 AM.


#117 brave_ulysses

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Posted 29 January 2015 - 07:15 AM

anyone else using toshiba sensors? the d5200 is the only one i know of...



#118 GJJim

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Posted 29 January 2015 - 07:53 AM

 

I thought the E-PM2 would be a great choice (and I can get one cheaply...)  and I think Jon's criteria (use the closest common full-well) is a good choice as well.  The pixels are quite small but surprisingly the full-well is decent.

 

However, I think that equivalent ISO (which is basically gain) and the pixel area should be figured in, and not just have a quality factor that is a % of each parameter - my Q1 parameter actually has a dimension and means something physically.

 

That said.. can the E-PM2 be tethered? Olympus web site only talks about the OM-D EM10 (or is it..)

 

The nice thing about the E-PM2 is that it doesn't need to be tethered. You can use a wireless intervalometer with it to sequence all of your exposures. It also has a very handy Bulb time mode that allows you to see the exposure gained so far during the entire exposure process. Basically it shows you what light it has collected every certain amount of seconds. That allows you to center even Dark D.S.Os without the need for a computer to control it.

The E-PM2 is a bargain at $370, but AFAIK there is no way to tether it for use as a remote-controlled astro camera. On a short tripod with a Polarie, composition and focusing would be a lot of "fun". It has a decent APS sensor, but is it really in the same league as the more capable bodies that allow for tethering or even wifi controls?



#119 mpgxsvcd

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Posted 29 January 2015 - 10:54 AM

 

 

I thought the E-PM2 would be a great choice (and I can get one cheaply...)  and I think Jon's criteria (use the closest common full-well) is a good choice as well.  The pixels are quite small but surprisingly the full-well is decent.

 

However, I think that equivalent ISO (which is basically gain) and the pixel area should be figured in, and not just have a quality factor that is a % of each parameter - my Q1 parameter actually has a dimension and means something physically.

 

That said.. can the E-PM2 be tethered? Olympus web site only talks about the OM-D EM10 (or is it..)

 

The nice thing about the E-PM2 is that it doesn't need to be tethered. You can use a wireless intervalometer with it to sequence all of your exposures. It also has a very handy Bulb time mode that allows you to see the exposure gained so far during the entire exposure process. Basically it shows you what light it has collected every certain amount of seconds. That allows you to center even Dark D.S.Os without the need for a computer to control it.

 

The E-PM2 is a bargain at $370, but AFAIK there is no way to tether it for use as a remote-controlled astro camera. On a short tripod with a Polarie, composition and focusing would be a lot of "fun". It has a decent APS sensor, but is it really in the same league as the more capable bodies that allow for tethering or even wifi controls?

 

Ask yourself “Why does a camera have to be tethered”. Seriously, what is it that tethering accomplishes? In my opinion it allows for easy organization of files, precise auto focusing, and near real time live view by slowing the frame rate down for cameras that are not capable of doing that without the tether(ie: unhacked Canon cameras).

 

I really don’t find the file organization to be that big of an issue. However, I realize that it is a chore for some people and they would like to automate that process.

 

Yes a program like BYEOS can get very accurate focusing. However, the 14x crop mode on the E-PM2 is a lossless crop. It literally extends the magnification out 14x from where you started. With my modest 800mm telescope that becomes an amazing 11,200mm. That definitely gives enough magnification to determine focus on planets or even dimmer stars.

 

That being said a fast scope helps with focusing tremendously. If you have an F10 scope most stars will not be visible in real-time. However, that is the case whether you are using a computer tether or not.

 

I also like using the four secondary vanes of my Newtonian to judge focus in the real-time cropped live view. It operates in a similar fashion to a Bahtinov mask and because it is real-time the lack of focus direction feedback is not an issue. You can quickly determine the point at which you have gone past perfect focus using the in camera crop mode. Then you can fine tune it and take one picture just to double check that everything is looking good.

 

However, the E-PM2 won’t give you that numerical reassurance that your focus is dead on. Instead you can easily achieve that result and confirm it with a picture. For those of us that are obsessive (Aren’t we all?) about this it may be an issue.

 

I actually think that the lack of a fast scope is more of a hindrance than the lack of computer control. Even with a computer tether a slow scope is going to make focusing with darker stars more difficult. It also makes centering of D.S.Os very difficult and time consuming.

 

I specifically chose an F4.0 scope to go with the untethered camera to make these things easy.

 

To answer your question directly. Yes! Absolutely the E-PM2 is as capable an A.P. camera as all of the other ones. Too many people have become fixated on the notion that if a Canon camera can’t do it with live view then no camera can do it with live view only.

 

The live view features(Bulb Time, Constant Preview live view out to 8 seconds, 14x lossless crop mode,….etc) that “ONLY” m4/3s cameras offer are what make them usable for A.P. without a computer tether.

Also the E-PM2 can usually be bought used for between $150-$225. I think that is about the same range that a used T2i goes for. Perhaps a little less. That isn't much money to spend to try it out.


Edited by mpgxsvcd, 29 January 2015 - 10:59 AM.


#120 mpgxsvcd

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Posted 29 January 2015 - 10:57 AM

The most important thing to realize is that we can sort the data in a number of different ways to promote any particular camera or feature that we want. We really need to determine what is important to us individually and then use the data that is given here to determine for ourselves which one is the best option for our own individual needs.

 

In my examples I took the Olympus E-PM2 from 2nd from last on the list all the way up to 2nd from the top by excluding some data that I specifically don’t trust and adding in other data like cost. Now I don’t really believe that the E-PM2 is the second best camera here. For instance I would choose the 6D if cost and usability were not factors.

 

In real world use every single camera on this list can produce stunning A.P. images. Some require more work, more money, or just more time to produce those results but all of them are capable of it. In fact most of these cameras in this list probably produce very similar results in 1:1 real world tests.

 

We have pretty much all of the data that we need now to make our own decisions and everyone is willing to help if someone does not understand what a specific factor represents. That is a very good thing and why this message board can be very successful.


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#121 tazer

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Posted 29 January 2015 - 11:24 AM

I find that 300s images @ ISO 800 end up in the right spot on the histogram on my NEX-5 (unfiltered, modified.) If I can reduce that exposure time to 150s or even 75s then guiding becomes unnecessary for me (at my focal length) especially if I can get my mount PEC trained to the approximate resolution of my imaging train. No guiding means no guidecam/OAG hanging off my focuser, fewer cables, no astro-imaging PC, quicker setup, easier alignment, etc...

 

Those shorter exposures means more savings, more objects being imaged in the same time frame, and less hassle (which equals more enjoyment.)

 

Everyone's needs are different but shorter exposures would benefit us all I'd think.

 

Mark



#122 mpgxsvcd

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Posted 29 January 2015 - 11:32 AM

I find that 300s images @ ISO 800 end up in the right spot on the histogram on my NEX-5 (unfiltered, modified.) If I can reduce that exposure time to 150s or even 75s then guiding becomes unnecessary for me (at my focal length) especially if I can get my mount PEC trained to the approximate resolution of my imaging train. No guiding means no guidecam/OAG hanging off my focuser, fewer cables, no astro-imaging PC, quicker setup, easier alignment, etc...

 

Those shorter exposures means more savings, more objects being imaged in the same time frame, and less hassle (which equals more enjoyment.)

 

Everyone's needs are different but shorter exposures would benefit us all I'd think.

 

Mark

The great thing about a fast scope is that you can image without the guider and in less time if you want. Or you can choose to use the guider with much longer subs if that is what you desire at that moment.

 

Getting a powerful focal reducer to work or any focal reducer to work with a large chip camera is much harder than getting a powerful barlow to work with the same camera. I always recommend starting out with a really fast scope and just adding in a barlow for more reach instead of doing the opposite and trying to get the focal reducer to work right.

 

Also the cameras of today have so much resolution it is easy to crop to 2x or more. There is absolutely nothing you can do with the camera to make your field of view wider. I much prefer a fast short focal length scope over a slow long focal length one.



#123 GJJim

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Posted 29 January 2015 - 11:54 AM

The great thing about a fast scope is that you can image without the guider and in less time if you want. Or you can choose to use the guider with much longer subs if that is what you desire at that moment.

 

 

Your description of the 14X magnified live view has almost convinced me to try one. The biggest headache for me is focusing. I have a setup with an old 5D, and at f/4 it's a challenge to get good focus even through a magnified right-angle view finder. What would you think about usability of the E-PM2 for eyeball focusing at f/5.6? 



#124 mpgxsvcd

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Posted 29 January 2015 - 12:03 PM

 

The great thing about a fast scope is that you can image without the guider and in less time if you want. Or you can choose to use the guider with much longer subs if that is what you desire at that moment.

 

 

Your description of the 14X magnified live view has almost convinced me to try one. The biggest headache for me is focusing. I have a setup with an old 5D, and at f/4 it's a challenge to get good focus even through a magnified right-angle view finder. What would you think about usability of the E-PM2 for eyeball focusing at f/5.6? 

 

It really just depends on what star you are trying to focus on. With anything bright (Sirius, Vega …etc) it is simple even with a slow scope. With darker ones it might be a "slightly" greater challenge. The difference between F4.0 and F5.6 is only 1 stop. These stars are usually MANY stops brighter than everything else.

 

I actually find it easier to get focus on areas where there are bright and dim stars very close together. M42 has a lot of those areas. The secondary vanes help as well.

What type of scope are you using?


Edited by mpgxsvcd, 29 January 2015 - 01:28 PM.


#125 tazer

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Posted 29 January 2015 - 06:58 PM

The 14X view on the Sony NEX is how I focus. I will use a Bahtinov mask at times but don't find it any more accurate than the live view. The trick is to not target a bright star but one that's just visible on the LCD. They tend to disappear off the LCD when not in focus, so it's easy enough to lock it in really quickly.

 

Mark




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