5 or 10 fps?

[jambouk]

In Mark Thompson's book (Astrophotography), he suggests inaging planets at 5fps when the seeing is good, and 10fps when poor.

Why is this? Do others follow is principle. He doesn't stipulate what camera he is using.

James

[Steve Ward]

Higher the better I'd say , you can then weed out the sub-standard frames with PIPP and still have plenty to play with.

In theory you can use a lower rate in good seeing , but how often do those conditions occur here in Blighty ... 

[Merlin66]

Freezing the few moments of "perfect" seeing conditions has been the Holy Grail of all photographers.....

A fast frame rate ( suggesting fast exposures - 1/60 sec or better) gives more opportunity of success.

Stacking and quality sorting programs like Registax allow you to maximise your chances.

[Cornelius Varley]

In Mark Thompson's book (Astrophotography), he suggests inaging planets at 5fps when the seeing is good, and 10fps when poor.

Why is this? Do others follow is principle. He doesn't stipulate what camera he is using.

James

This probably goes back to imaging with a webcam when the max fps you could get without compression was 10 fps. Under ideal conditions it is better to image at the lower frame rate and use the faster framerate when conditions are not ideal.

[jambouk]

CV, but if the compression is/was the same at 5fps and 10fps, why reduce frame rate when the seeing is good and only collect half the amount of data? That is my confusion.

James

[davedownsouth]

I thought there were planetary cameras out there now capable of running at 60 - 200 fps.  5 / 10 sounds very slow 

[Cornelius Varley]

I thought there were planetary cameras out there now capable of running at 60 - 200 fps.  5 / 10 sounds very slow 

5 / 10 fps was typical of webcams such as the SPC900

[Cornelius Varley]

CV, but if the compression is/was the same at 5fps and 10fps, why reduce frame rate when the seeing is good and only collect half the amount of data? That is my confusion.

James

When webcams ruled at planetary imaging 5 fps used to be typical for good seeing conditions, the atmosphere was stable and the imager could take their time capturing data. Under poorer conditions 10fps was used to capture the fleeting periods of good seeing.

[jambouk]

I'm still not understanding why 5fps when the seing was good was regarded as adventageous over 10fps.

James

[Cornelius Varley]

Even at 10fps there might be data compression so it better to image at the slower framerate when conditions allow.

[Steve Ward]

Could also be something to do with the somewhat smaller capacity of computer storage 'back in the day' ... 

No 3Tb hard drives then.

[webtubbs]

Longer exposure per frame, perhaps? Good seeing (i.e., stillness) allows longer exposures so not as many frames would be required. Bad seeing on the other hand requires very short exposures, so more frames would be required.

[Kokatha man]

James, Peter (CV) has really addressed some of the "conceptual" aspects of said tenets...I say "conceptual" because the sort of information you have read is not only an idea rooted in understandings that are way out of date (leaving aside that they were written for the Toucam) but more importantly technology &  knowledge  have far out-stripped said cameras & approaches...

Before anyone tells me what fine cams the Toucam series were I'd like to say that I agree - for their time!

Forget the out-dated books etc, in fact forget about paying anyone for information (hopefully you didn't purchase that particular book!  .)..there are plenty of good planetary imagers on forums more than happy to assist with their experiences using a large range of planetary cameras...

[jambouk]

Thanks again all.

I did buy the book but it was only about a fiver and it was for my society's library, i just wanted to have a quick read first We have plenty of members who still gather information and help from books rather than the internet, and some who don't have access to the internet. Also very few own dedicated planetary cameras and who use modified webcams, so this kind of book is ideal to get people going on the right path.

I guess the longer exposure idea is a possibility, I'd have to check sharpcap logs to see what sort of exposure settings i've used with my logitech as 200ms sounds quite long for Jupiter, but this could be a factor.

The compression thing is what i suspected would be the answer but wanted to hear if others commented on it. This goes back to a question i asked over a year ago but never got a solid answer... How can one tell how much compression is occurring at different frame rates?

Thanks

James

[sharkmelley]

I'm still not understanding why 5fps when the seing was good was regarded as adventageous over 10fps.

James

I think it is a question of Signal to Noise ratio.  If read noise is the main contributor to the overall noise (which is certainly was with those webcams) than 1 frame taken at 5fps will be cleaner than 2 stacked frames taken at 10fps - because the 2 stacked frames have 2 helpings of read noise.  In fact you might need 4 frames at 10fps to give the same SNR as 1 frame at 5fps - so at 10fps you end up needing twice the total imaging time to obtain the same SNR. If the seeing is not stable enough to produce sharp frames at 5ps then 10fps would be used and the final image would be noisier and sharper.

Best advice for obtaining the best SNR is to use the slowest frame rate that conditions will allow.

For selecting the best planetary imaging camera then apart from frame rates, I reckon the most important information is the QE (quantum efficiency) and read noise because these will determine the ultimate signal to noise ratio.  But I've never seen such useful figures published.  We have to rely on assertions that camera X is better than camera Y without the supporting data. 

Mark

[Steve Ward]

For selecting the best planetary imaging camera then apart from frame rates, I reckon the most important information is the QE (quantum efficiency) and read noise because these will determine the ultimate signal to noise ratio.  But I've never seen such useful figures published.  We have to rely on assertions that camera X is better than camera Y without the supporting data. 

Mark

 Guess you've never seen Piotr's website then ... 

http://www.rkblog.rk.edu.pl/astro/kamery-ccd/

[Kokatha man]

Thanks again all.

I did buy the book but it was only about a fiver and it was for my society's library, i just wanted to have a quick read first We have plenty of members who still gather information and help from books rather than the internet, and some who don't have access to the internet. Also very few own dedicated planetary cameras and who use modified webcams, so this kind of book is ideal to get people going on the right path.

I guess the longer exposure idea is a possibility, I'd have to check sharpcap logs to see what sort of exposure settings i've used with my logitech as 200ms sounds quite long for Jupiter, but this could be a factor.

The compression thing is what i suspected would be the answer but wanted to hear if others commented on it. This goes back to a question i asked over a year ago but never got a solid answer... How can one tell how much compression is occurring at different frame rates?

Thanks

James

Apologies - for some reason my pc took me to this section of SGL instead of the "Planetary Imaging" section where I normally post on SGL - & only realised it just then when I wondered what had happened to this thread ...

It probably explains why I thought/think this discussion is a bit like "re-inventing the wheel" or perhaps more in line with "what are the benefits of a quinquereme over a trireme...and what benefits does rowing the quinq at 5 strokes per minute give as compared to 10spm's..!"

I appreciate that there are still a lot of folks not using the internet etc James - but tbh when it comes to subjects like planetary imaging soliciting information from publications that are not only out-dated/irrelevant/inaccurate, one should be extremely circumspect to say the least..!

As someone who has had the privilege of being ZW Optical's *ahem* "freebie-induced tester"  since they began producing planetary cameras...& having utilised PGR & IS cameras before these right back to the Toucams in question I think I can speak with a small amount of authority on these matters...when we were the first people outside Mainland China to utilise these cameras & start imaging Mars at 250fps & Saturn at 170fps it certainly created similar debate in many ways to this "5 or 10fps" thread's thrust...but our images were undeniable in their outcomes: the world has moved on a lot since then even...which with all due respect was the thrust of my earlier posting.

As to actually determining "compression" then (1) avoid it if at all possible (which is why most of the latest cameras are usb3 etc) (2) calculate the data rate in kb/s (or mb/s!) & measure this against the specific data conduit's transfer capabilities.....the old Toucams did have problems there & if you consider we download data at the rate of 6.4MB every 100 seconds for Saturn you get an idea of the demands of current technology...I'll plug a drive of old avi's in later & check the comparable rate with the Toucam for Saturn if you'd like...

[Zakalwe]

A slower framerate may mean less gain is used, hence less noise in the final image. However, this is partially balanced against a higher framerate will capture more frames and the stacking process will use those extra frames to reduce noise in the final image.

Whatever camera you use, try and get the histogram at about 60-70%, the gain as low as possible and the framerate as high as possible. It's a balance between those three competing variables. get the gain too low and you'll get onion-ringing. Get the histogram too high and you'll blow any highlights out in stacking and processing.

The specific info in the book sounds very out-dated. The overall concepts are probably sound, but the specifics have been completely surpassed by the march of technology. Look at some of the latest camera- 300 frames per second!

[Kokatha man]

Whatever camera you use, try and get the histogram at about 60-70%, the gain as low as possible and the framerate as high as possible. It's a balance between those three competing variables.

...while I agree with some of your comments Zak it is nowhere near as simple as what I've quoted from your post...the ASI174MM operates at much lower histograms than your suggestion...we employ 21%/19%/17% for r/g/b on Saturn & this particular planet is extremely demanding re surface detail resolution...and although it is a tad arrogant to state,  I am unaware of any other AA'er achieving the sorts of  repetitive surface detail confirmation on Saturn that images such as this animation http://stargazerslounge.com/topic/243927-the-r-rgb-saturn-image-enhanced-animation/page-1 resolves/displays.

In fact, as most folks would know our mantra is "don't worry about having to maximise gain, try & achieve the maximum possible frame-rate sustainable with an appropriate histogram for any particular camera.* 

* eg, the ASI120MM-S operated quite effectively with 30% - 40% histograms...the newer ASI174MM at the aforementioned values...

[Zakalwe]

...while I agree with some of your comments Zak it is nowhere near as simple as what I've quoted from your post...the ASI174MM operates at much lower histograms than your suggestion...we employ 21%/19%/17% for r/g/b on Saturn & this particular planet is extremely demanding re surface detail resolution...and although it is a tad arrogant to state,  I am unaware of any other AA'er achieving the sorts of  repetitive surface detail confirmation on Saturn that images such as this animation http://stargazerslounge.com/topic/243927-the-r-rgb-saturn-image-enhanced-animation/page-1 resolves/displays.

In fact, as most folks would know our mantra is "don't worry about having to maximise gain, try & achieve the maximum possible frame-rate sustainable with an appropriate histogram for any particular camera.* 

* eg, the ASI120MM-S operated quite effectively with 30% - 40% histograms...the newer ASI174MM at the aforementioned values...

I stand corrected.

I've only recently bought my frst ZWO and have only tried it on solar.

In fact, as most folks would know our mantra is "don't worry about having to maximise gain, try & achieve the maximum possible frame-rate sustainable with an appropriate histogram for any particular camera.* 

That's the point that I was trying to make. I used to use a DMK21-618 camera and I found that I got better results by getting the histogram in the right place and going for frame-rate. The extra noise caused by a higher gain was compensated for by the increased number of frames that could be stacked.