2339 replies to this topic

[mmalik]

Jon, the option you describe will be quite similar to #5 in the mod choices listed here..., where you replace the 'only/default' stock filter of a7R with a modified (LPF-2 replacement) one. [Note: This is the reason I keep thinking in terms of LPFs even for a7R, will touch upon this more in coming posts as to why?].

 

 

Yes, it can be done but the architecture of alpha sensor assemblies is such that one would be better off NOT going that route for a7R, and for that matter all alphas (a7S, a7/a7II).

 

 

My original point... was that the "advantage" one gets from 'high quality' stock LPF-1 of a7S or a7/a7II is NOT there in a7R, hence option #2 of the mod choices... is also not there for a7R. Hope I didn't confuse the matter. Regards

Edited by mmalik, 05 February 2015 - 12:04 AM.

[Jon Rista]

I may just be confused about your use of LPF. LPF is Low Pass Filter, a blurring filter. LPFs are designed to blur. One of the benefits that I see for cameras without an LPF of any kind is they don't do any blurring. Final output resolution is a result of convolution...the blurring caused by each and every "optical" element between your subject and the sensor. That includes the atmosphere, lens or telescope elements, LPFs, etc. Even though it's small, an LPF is still going to add it's blur to the image. Not that helpful at large image scales, but if you are imaging at a smaller image scale (such as in my case, my image scale is 1.4x at 600mm, definitely not oversampled...and even less so given the bayer array), the lack of any kind of aa blurring would be very beneficial. 

Since there is no LPF in the A7r, it seems to me you have three options:

1. Do nothing (and suffer lower Ha sensitivity)
2. Full spectrum (and suffer star bloat due to IR)
3. Astrodon Glass Mod (No bloat, gain Ha sensitivity)


 

[ccs_hello]

http://www.sonyalpha...g-pixel-sensor/

 

RE: photon counting pixel sensor RUMOR

 

Fake info with lots of incorrect descriptions (in both diagram and text) and the "creator" didn't even understand how CMOS APS really works.

 

Clear Skies!

 

ccs_hello

[mmalik]

Jon, I have fixed my previous post... since a word ('equivalent') was not a good choice on my part and may have led to some confusion.

 

 

Here is the disconnect I see... you are using LPF in more literal/functional sense, and I am using LPF it in physical sense from mod perspective as I open the camera—what's sitting where, which filters are bonded together, etc.

 

 

I suggest we call LPF-1, 'Filter-1' and LPF-2 'Filter-2' and refer to their replacements as such; following diagram will clear the concept in terms of a7R vs. standard configuration (a7S for example).

 

 

Note: What this all means is that LPF-2 becomes a component of 'Filter-2' complex when present; when NOT, the remaining components make up 'Filter-2', as in a7R.

 

 

Regards

 

 

Source: Own rendering

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Edited by mmalik, 05 February 2015 - 04:21 AM.

[garret]

Posted 03 February 2015 - 10:17 PM

A quick side by side comparison of a7II/a7S/6D:

Data source: DXOMark...

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@mmalik, It looks like you getting a nice collection of  DSLR camera's for Astro imaging, but do you actually use these camera's? do you or can you test these camera's

in the real world; under the stars?

 

In this section of Cloudly Nights ( DSLR Camera's, Astro imaging & Processing), there is a endless debate about noise, readnoise, QE, ISO, filters, APS, FF, LPF, whatever...

The next time you should buy 2 or more second hand 66mm refractors (the model with SCT tread on the focuser tube), mount them side by side on a mount, and perform

a side by side comparison for the camera's under the sky.

You only have to collect a handful of subs to get real-world-data from the camera's, then make the raw data available to anyone for processing.

I bet we will be surprised for the results!

 

 

Garrett van der Veen

 

 

 

[mmalik]

Garret, I am more anxious to test these cameras; my backlog is growing. I have yet to test 7DII, a7S and a7II.

 

 

My problem is this... there is quite a bit of snow outside, temperatures are bitterly cold (-11F [-24C] wind chill as I write this...), and if that wasn't enough a full-moon I might add . Cloudy nights is whole another story.

 

 

I am afraid it is going to be a while before I can take some decent subs and share with you folks; will do it upon my first opportunity. Thanks for your understanding. Regards

Edited by mmalik, 05 February 2015 - 05:36 AM.

[garret]

My problem is this... there is quite a bit of snow outside, temperatures are bitterly cold (-11F [-24C] wind chill as I write this...), and if that wasn't enough a full-moon I might add .

 

The most worst case of  light pollution is full moon +  snow cover + some moist in the sky, in such case I do not image, and tonight I have... a near full moon and a snow cover, but the air is very clear and dry: the moon is blazing!

 

Garrett

[Jon Rista]

Thanks, Mike. I do think using the terms Filter-1 and Filter-2 is better. LPF does bring with it a specific connotation, and not all cameras have LPFs.

 

So, I still don't fully understand why replacement of the A7r UV/IR filter ("Filter-2" according to your paradigm) and replacing it with an Astrodon UV/IR filter is undesirable. What are the consequences of doing that?

[mmalik]

Back in the Pre-A7R era, factory Filter-1 (which is missing in a7R) was considered 'enough' for IR/UV blocking, it allowed 100% H-alpha transmission, and was also considered of superior 'build quality' than after market Filter-2 replacements. In other words, after market Filter-2 replacements were considered either redundant or un-necessary while factory Filter-1 was still in place for Pre-a7R era DSLRs.

 

 

I say this without getting into the thickness, refractive index, pass-band, internal reflections, and other ramifications of after market glass of any kind that goes "inside" the camera.

 

 

a7R has shifted the paradigm; yes, one may replace stock a7R Filter-2 with after market Filter-2 replacement, but it may not match the build quality of factory Filter-1, had a7R had one to begin with.

 

 

Best option for a7R may be to go full-spectrum which has its dependencies in external IR/UV blocking, CWB, etc. Hope this helps. Regards

[Jon Rista]

Hmm...it would be interesting to see how much Ha is actually passed by the A7r Filter-2. From the standpoint of human-centric color balance, most cameras have a filter that causes a gradual falloff into IR, which usually results in 20% or less Ha sensitivity. Since the Astrodon filter passes well over 90% Ha, it seems for an astro mod, it would be beneficial...even if the build quality is not as high as the default Filter-2.

 

It's Astrodon, though...they make some of the best astro filters on the market (THE best, even?)...might at least be worth a try. They aren't that expensive.

Edited by Jon Rista, 05 February 2015 - 05:37 PM.

[mmalik]

No harm trying

 

...might at least be worth a try.

 

Yes, no harm trying. Regards

[mmalik]

a7II size perspective (which is little bulkier than a7/A7S/a7R).

 

7DII is the bigger one...

 

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[mmalik]

a7II 5min darks, ISO 3200, ~70F

 

Note: Images are very small sections of the centers of in-camera JPEGs at 100% zoom; complete RAWs/JPGs of a7II are located here.... Regards

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Edited by mmalik, 08 February 2015 - 07:20 AM.

[mmalik]

Contrast above with a7S, 5min darks, ISO 3200, ~70F

 

 

Note the 'standard' reddish mottle of a7S vs. 'standard' whitish mottle of a7II above; any thoughts on the difference?

 

 

Note: Complete RAWs/JPGs of a7S are located here...

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Edited by mmalik, 08 February 2015 - 07:37 AM.

[mmalik]

Sony a7II Settings for Astrophotography...

 

[AnakChan]

This is interesting (do note I'm reading straight off the iPhone coming home from the camera store after picking up an A7s). It seems the A7ii looks cleaner than the A7s?

I'm thinking of CentralDSing my A7s & still have an opportunity to change. If both are cooled I wonder if relatively the difference between the two would still be the same.

I'm questioning my A7s choice for cooling after reading your findings.

Aside from noise though, would the A7s still be more sensitive than the A7ii? In other words, for my light frames from the A7s, I may not need to expose for as long as the A7ii, or do I still?

[mmalik]

I'm questioning my A7s choice for cooling after reading your findings.

 

Aside from noise though, would the A7s still be more sensitive than the A7ii? In other words, for my light frames from the A7s, I may not need to expose for as long as the A7ii, or do I still?

 

As you already know..., with Central DS mod you'll not be able to use the shutter since sensor is moved in front of the native shutter; 'Silent Shooting' disables Bulb mode in a7S, a big drawback! I still don't understand what kind of mod they do to the sensor (i.e., which filter?) Given the sensitivity of a7S, using it in somewhat cooler climates may not require invasive cooling, which is also quite mutilating.

 

 

About a7II, I feel a7S probably would still be more sensitive than a7II, main difference being more resolution in a7II for shorter FLs. Regards

Edited by mmalik, 08 February 2015 - 06:15 AM.

[AnakChan]

So talking to Jack2338 offline, it seems one can get longer exposures with a remote. Yes whilst this does depend on the mechanical shutter (which is redundant in this case), one could fall back to the "black card in front of the lens" routine which will act as the mechanical (& manual) shutter.

 

at least in the 80s I used that regularly whilst waiting for shutter vibration to dampen down.

Edited by AnakChan, 08 February 2015 - 07:06 PM.

[ccs_hello]

RE:  As you already know..., with Central DS mod you'll not be able to use the shutter since sensor is moved in front of the native shutter; 'Silent Shooting' disables Bulb mode in a7S, a big drawback!

 

That's a ugly mod.  Really should wait CentralDS does it right in the future.

 

Edited by ccs_hello, 08 February 2015 - 08:33 PM.

[AnakChan]

So talking to Jack2338 offline, it seems one can get longer exposures with a remote. Yes whilst this does depend on the mechanical shutter (which is redundant in this case), one could fall back to the "black card in front of the lens" routine which will act as the mechanical (& manual) shutter.

 

at least in the 80s I used that regularly whilst waiting for shutter vibration to dampen down.

 

I've got some update from CentralDS. In Silent Shuuter Mode Off (ie. mechanical shutter), the exposure process is what is believed to be :-
 

1) Mechanical shutter open

2) CMOS exposure starts
3) Mechanical shutter closes

4) CMOS exposure finishes

5) Data transfer

 

In the case of the Astro A7s, whilst the mechanical shutter isn't practically used as it's behind the CMOS the workflow doesn't change :-

 

1) (Redundant to exposure) mechanical shutter opens

2) CMOS exposure starts

3) (Redundant to exposure) mechanical shutter closes (but in this case CMOS still receiving light)

4) CMOS exposure finishes

5) Data transfer

 

The only concern I may have here is between (3) & (4), is vibration from the shutter close as the CMOS is still recording light during this phase. Maybe back to the black card routine.

 

I have to say though if that's how the A7s mechanical exposure works, I wouldn't have thought it'll work that way. I thought the CMOS would start recording before and after shutter opens/closes and leave it up to the shutter to determine the actual exposure duration.

[mmalik]

Most alphas' (including a7S) standard (non-LENR) exposure sequence is more like this:

 

 

1. Shutter is already open (Live View is active)

2. Live View ends (Shutter remains open)

3. CMOS exposure starts

4. Shutter closes/CMOS exposure ends [Don't know which happens first? Or in sync?]

6. Shutter opens and remains open

7. Live View resumes...

 

 

Corrections welcome!

[mmalik]

While we are on the subject, a look at a7II stock sensor

 

 

Note: Contrast this with stock a7S...; I wonder what causes such significant color and look/feel difference?

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Edited by mmalik, 09 February 2015 - 06:11 AM.

[mmalik]

A look at a7II shutter

 

 

Note: Contrast this with a7S...; note bit wider cut of a7II shutter window

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Edited by mmalik, 09 February 2015 - 06:09 AM.

[mmalik]

MILCs may not have mirror slap (no mirror...), but they surely seem to have pretty noisy/violent shutter slap. Loud shutter of a7II have startled my quite a few times as exposures end. To me it appears closing slap is more noisier/violent than the opening one. I can tell the difference since shutter opens quite softly at the end of an LENR dark; but on a non-LENR exposure, exposure ends with a pretty aggressive and quick shutter close & open sequence, bulk of noise coming from shutter closing than opening. Regards

Edited by mmalik, 09 February 2015 - 06:28 AM.

[mmalik]

In my exchange with Jim Kasson..., he suggests following ISO settings and NOT going above them; your thoughts? What does it say about major vs. minor ISO stops [...for lack of proper terminology?]

 

 

a7II.................ISO1000

a7S..................ISO2000

 

 

Courtesy of Jim Kasson... (Claff PDR vs. ISO setting as ratio to ISOless camera)

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Edited by mmalik, 09 February 2015 - 09:27 PM.