Jupiter with Nexstar 102slt and cheap webcam!!

[Clayton]

Neil, Im a little confused by the terminology here?? When you refer to "fps" are you referring to shutter speed or the number of frames per second that the system records, or something else?

The way I understand it fps=the number of individual frames that are imaged, or exported from the camera, or are recorded to the HDD (usually in avi format) per second.

Shutter speed is the length of time each frame is exposed for, ie. 1/25 sec = a longer exposure than 1/1000 sec which is shorter and more suited to freezing movement.

Of these two it is shutter speed that affects the brightness and ability to freeze movement. Whereas fps is merely the number of frames captured or desired to be captured and has little or no effect on image brightness? or need for gain?. As was mentioned earlier if you try to extract the data from a CCD too fast it will introduce noise or in some cameras compression artifacts will appear.

Personally my system seems happy with about 10 fps and will perform from 1/30sec to 1/250sec with no ill affects (I had problems but they seem fixed now??) apart from the increased noise from the gain I have to use at 1/250th. I find that 1/30 is too slow to freeze the seeing for me on usual nights but 1/50 is a good compromise. 5 frames/sec has no benefit for me or no ill effect unles I am trying to image Jupiter where I prefer to gather as many frames in my given time before the (much maligned) rotational blurring kicks in. 10 fps gives me 1200 frames in my usual 2 min's that is enough for my ageing system. If I was running modern cameras and laptop I would certainly be trying to up the fps to the point when I began to lose quality.

Sorry to rabbit on so much but that is my understanding of how it works, which my experience supports. It may be that your terminology is different, or that your experience has led you to this(different from mine) understanding. Which is OK as well. "Whatever works" is one of my mantra's. I simply ask so that I know if we are reading from the same manual (so to speak)

[neil phillips]

Hi Clayton yes i mean frames per second captured, and it does have a direct effect on gain. going from 30 fps to 15 fps because of the exposure change that would accompany a fps change like that,

Sorry i should have made myself clear the exposure would change when dropping to 15 frames per second needing less gain and hence smoother higher quality frames.

The only downside is at 15 fps the camera reacts more slowly to rapid seeing changes, A fair price for a 50% reduction of blured frames during processing and the quality estimation error i mentioned in my post. Registax also has this error Clayton indeed i know many who are switching to avi stack for lunar because of this problem that im highlighting here. Read my post again and it should make more sense

[Clayton]

Sorry Neil I still don't get it. Exposure is not reliant on fps in any of the several different webcams I have used, except in the case where the exposure is longer than the fps. I nearly always run 10fps but vary my exposure widely (1/30th to 1/250th). I understand if you wish to expose at 1/15th then you would have to drop the fps to 15 fps (or less) and you could then lower the gain, but that would be as a result of the longer exposure and not lower fps. And lower fps should not blur the image, as seeing comes and goes and on average you would get the same number of sharp frames as blurred ones if you captured the same total number of frames. If you were exposing at 1/15th however you would surely get blurred images and a blurred stack, unless the seeing was very good.

[tooth_dr]

After reading this whole thread I'm now really confused about the whole fps, and exposure time business. I've been using vlounge with my toucam, but recently downloaded wxastro, and have not yet used it in anger. When I image with vlounge I set it to 10fps, then adjust the shutter speed and gain accordingly. I always assumed fps and shutter speed were intrinsically linked but this doesn't necessarily have to be the case.

[rawhead]

After reading this whole thread I'm now really confused about the whole fps, and exposure time business....

Join the club!

[neil phillips]

Ok what i mean is for example if i wanted to change the exposure from 1 /30 secs to 1 /15 secs to attempt a higher quality, less grainy per frame capture. ( by reducing gain a lot ) to get such said reduction of grain on jupiter then the frame count would have to drop.

[so there is indeed a relationship between fps, exposure, and gain,]

you can not affect one without affecting the other. shooting a planet and keeping healthy levels. otherwise your levels would go to pot

without altering the exposure you would not be able to reduce the gain. otherwise the levels on jupiter would be to dim. so of course at 30 fps if i wish to reduce gain a lot, lets say as my example to 1/15th secs exposure ,then the frame rate would have to drop to 15 fps you can not affect one without affecting the other

I already mentioned its the quality estimation error on registax or k3 that is causing the blur. not the capture

but my point was at 30 fps the amount of stacked error would be twice that of 15 fps as there is half the frames. so by dropping the frame rate to 15 fps and lets be clear about this to 1/15 secs exposure, to keep the levels the sames as i would have had at 30 fps and 1/30 secs exposure, the gain can now go down significantly producing a higher quality smoother less grainy capture. with each individulal frame being much less noisy AND LOWER ESTIMATION ERROR because of a reduction in stacked frames

[neil phillips]

By talking about dropping the frame rate and reducing gain for less grain. i assumed you would figure i would be altering the exposure otherwise jupiter would most likely be too dim. Probably not explaining myself clearly enough. Apologies

[neil phillips]

QUOTE=neil phillips;1310060]Hi Clayton yes i mean frames per second captured, and it does have a direct effect on gain. going from 30 fps to 15 fps because of the exposure change that would accompany a fps change like that,

Sorry i should have made myself clear the exposure would change when dropping to 15 frames per second needing less gain and hence smoother higher quality frames.

Ive never seen the exposure change by itself, i meant adjusting the exposure to achieve lower gain, i can see how you thought i let exposure do it all by itself. which it does not, By my uncareful wording.

And yes your right, but i mentioned that by going to 15 fps from 30 fps it wouldnt cope with the rapid seeing changes as well. Meaning an exposure change too.

when i talk about lowering frame rates its always as a consquence of adjusting exposure thought that would go without saying

But i said its a trade off that by reducing the amount of frames during stacking, it seemed like a trade off that was less important. Because of the very damaging bluring effects that quality estimation errors, that both registax and k3 produce.

so much so, others are switching to avi stack. I also mentioned by removing the quality estimation errors by hand, at 30 fps, would indeed reverse these bad blurring effects, But Its not somethling i like doing, even when trying to speed up it using frame deletion on virtual dub for example.

2 mins which is vergiing on rotation blur i know, but was the capture time i was using at 30 fps this night, is a lot of frames to go through, deleting the quality estimation errors that are much talked about now on registax.

The up shot is by not manually removing them the 15 fps 1/15th sec capture showed finer detail with less smearing and bluring,

Than 30 fps captures ( and i took a few )

and im guessing here, i think its the quality estimation errors that caused this stack to be better.

Actually should say a lack of them. probably by half as there was half the amount of frames for k3 to get slightly wrong if you see my point.

I said carfull study will either confirm or refute this. But of course whats really needed is better quality estimation.

Something else ive been thinking does two noisey frames more than make up for 1 less noisey, another important question. relating to exposure fps and gain choice.

When i tried 60 fps yes at 1/60 secs, a while ago on jupiter it defiantely did not, despite the rapid seeing changes being coped with at 60 frames per second. 1/60 secs

[Clayton]

OK Neil Now I understand a lot more

Sorry for being so pedantic, and thanks for being so patient.

I still have some questions but have to rush off to work just now so I will ask later.

[neil phillips]

No worrys Clayton i need to stop assuming that others know what i mean by being broad in my terms. But obviously one wouldnt drop frame rate for no reason that would just lose data, which is why i assumed others would know what i mean. But looking back it is confusing i agree. again apologies.

I think i will try captures at lower frame rates and different exposures other than 30 fps. to see if this wasnt a one off. as i already said it may have been a effect of better seeing at that moment, or my focusing may have been tighter, just to understand if im assuming right about these quality estimation errors. but if i am right, then the combined effects of these errors are so damaging that unless a way can be found to remove them quickly then smaller stacks with smoother frames seems a advantage.

Which i admit is at odds with what ive always belived and probably only under good seeing would it work any way. I need to experiment at 1/23rd 1/19th 1/15th to see the effects. as per my usual 30 fps 1/30 secs settings at the magnifications ive been trying to achieve, gain is pretty much maxed out with those settings. Apologies Gavin think ineed to be discussing this elsewhere

[Clayton]

Yes. Sorry from me as well Gavin. I would like to pursue these issues further and hand your thread back

[Taff]

Hi Gavin' that's a nice picture with the belts on show.Mark