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My recollection is that Martin Mobberley's Planetary Imaging book suggested that the better planetary imagers of the time were using f-ratios of f/35 to f/40. The game is changing and I do agree with Darryl's posting from the other day suggesting that f/20 is probably nearer the mark for cameras such as the ASI120, but they have a much smaller pixel size than the 5.6um of the SPC900 and DxK21.

James

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Took this at ~4.30 on 19th Feb. 5 min AVIs per colour at 15fps. Stacked ~1000 in AS!2 then R6, WinJupos and PS. Was very lucky with the seeing though there was a bit of mist in the air hence the low f

Thanks guys. I was pleased with how it came out but have had a bit of a reprocess and calmed it down a bit. These are the RGB files (after processing) that I captured. It is the blue as expected that

Thanks for the comments guys. Chris, that's with the stock focuser. At these high focal ratios, there is a reasonable range of critical focus position. I only use the CPC for planetary work so don't h

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I don't think f/40 is too extreme in some circumstances, especially with a DMK/DFK. I was getting up to around f/35 with the SPC900 last Spring when I was imaging Mars. Certainly for the pixel size of those cameras the maths doesn't make it look unreasonable.

As the pixel size comes down of course smaller f-ratios can achieve just as much.

In theory, anyhow :)

James

James you need to man up I was imaging Mars at f56 last year. :cool: Seriously though Mars was high and bright but Saturn is low and dim so f40 sounds crazy but evidently Freddie has worked some magic with this method. I've seen others on the CN forum use 30% Histograms it seems Saturn can take these low levels. Its all food for thought and just shows what can be gained from experimentation and perseverance.

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Ah, it was you, was it? I knew someone was working at those kinds of focal ratios last year, but I couldn't recall who.

There is certainly a balancing act to be done here. The theory might say for a given sensor that f/40 is the optimal focal ratio, but if the telescope isn't big enough to deliver the photons to provide a decent image at the required frame rate then it's never going to end happily :)

James

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Thanks for your comments Jam1e1 and Theo.

Neil, Stuart, When I got my 4x I did think F40 was going to be for very special nights only, but I actually use it most of the time. All my RGB Jupiter shots are also F40. I try and keep the exposure as short as I can by using highish gain but the one thing I don't worry too much about is having 35-40% histo. which most people would say is a really bad idea. This allows a shorter exposure and higher frame rate obviously and I find that for any given conditions it is more important to get the short exposure than aim for 60-70% histo. Obviously conditions were good on the 19th but I apply that logic all the time. As I said earlier, I then do a stretch after stacking (having selected all alignment points manually as I think it gives better results than the auto option) as R6 will do an autostretch on low histo stacks even if you tell it not to and it over does it. Have you ever noticed that? I was surprised when I noticed it. I would never normally stack less than 1,000 frames, but lacked enough good B ones and I would rather stack fewer good ones than add bad ones to the stack.

A bit of careful processing in R6/WinJupos and PS and you can usually overcome the effects of high gain and low histo. Obviously good seeing (which I clearly had on the 19th) is important but you may want to experiment with some lower histo captures.

I use ICcapture and doing the math was capturing at ~9fps R&G and ~7fps for B. The whole process took about 17 mins to capture but doesn't look like that has caused too many issues though there is a funny line on the left side of the planet if you look.

Anyway, lots of processes that go against convention but I think have worked ok on my Jupiter shots as well as this Saturn.

H Freddie, no i wasnt suggesting F40 was too much, i have ALMOST pulled off over double that on Mars using a 5x powermate and 2x ultima plus filter wheel.

http://www.flickr.com/photos/16601714@N04/8361246773/sizes/o/in/photostream/

But I was certainly surprised you did it at 24 degress at those very slow exposures with such a fine result, thats what took me back the most.

I also dont worry too much about a very healthy histo. I went into length about this recently on my Saturn post. Though i think 50% is optimum on Saturn, but at 30 fps i was less than that recently. So i agree with you there intirely. It is better to have a very healthy histo if you can get it. But ive always found slowing the exposure down at my location is just bad news Unless seeing is very good .

I am suspecting your location might be better than mine Judging from your settings and result here.

I do a stretch on AS/2 i dont sharpen on R6 mainly because i dont do de noise, i prefer to cope with noise otherways. So i use R5 i havent seen any increase on R5.

Strange you get 9fps with with a exposure less than 1/15th secs exposure.When i do that it drops to much lower. ive found i have to set it to around 7 frames a second. I wonder how you get more. do you punch in the frame rate you want. If so i didnt know you could do that. Or do you set it to 15fps At 1/13th secs exposure what frame rate do you set ?

Anyhow. I will certainly experiment with slower exposures. But as mentioned seeing will have to be good im sure. I dont think a image and settings has surprised me as much as this one for quite some time. Its not that i dont understand the logic of all this. Just i found at my location these ideas generally havent worked. when ive tried. But as mentioned i suspect your location might be delivering slightly better than mine. Just hoping for some good seeing to try out a slower exposure. I will also do some at 30 fps. if it doesnt work out for me as well as it did you here

I cant say great job enough

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Not hijacking your thread Freddie but i have a question for you & Neil, my laptop has usb, the usual windows gumf running & not much else when imaging, when i select 60fps sometimes it seems to drop a lot of frames ie when i watch the counter it will get to 10 secs & ill only have 400-500 frames not 600, this has happened imaging Jupiter & the other night trying Lunar, is this down to object brightness, optic size, 3x barlow in train too much for transparency or just me ?, i would have thought Lunar imaging would easily achieve 60fps & more so i am a little stumped.

I appreciate with Saturn it's position & brightness overall will effect what fps you can get & it makes sense to go low for fairly good seeing, is the imaging time about the same as Jupiter ?, Saturn - 10.5 hrs, Jupiter - 10 hrs ?

Appologies again Freddie but as i follow your's & Neil's work i thought you could both provide some answers.

Ewan

Sorry Neil i have just seen your reply on your thread i posted on re barlow, i have been slow in checking on replies :-(

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Thanks for the comments guys, much appreciated.

That's a nice shot of Mars, not sure I will ever be brave enough to put my 4x and 2x together. I do shoot over the top of houses but they are not particularly close and being in a large village there are not that many of them. I'm in no doubt that the general conditions and seeing that morning played a big part in this image.

Neil, I'm not sure how well known this is but the IS cams have two internal modes of operation. I have no idea why. If you set the exposure shorter than the frame rate e.g. 1/40sec 30fps the cam takes the exposure and delivers to the computer to save in parallel. If you set the exposure to be longer than the frame rate e.g. 1/40 sec 60fps the cam takes the exposure then delivers to the computer to save in series. In this mode you obviously then end up with fewer frames than you would expect per second. If you match the exposure and frame rate e.g. 1/30sec 30fps the cam will operate in parallel mode, but you have to force it to switch by first setting a shorter exposure and then selecting the actual one you want. I must admit I sometimes forget this myself in the heat of the moment (or should that be cold!!!)

In terms of the exposure, you can only select the fixed options given by the cam but I always try and remember the above to maximise the number of frames being delivered to the laptop.

Ewan, there is not only the above to take into account but also check that your computer is not doing something else when you are capturing. Having security progs running or background checks can slow things down and limit the number of frames that end up being saved during a capture.

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Not hijacking your thread Freddie but i have a question for you & Neil, my laptop has usb, the usual windows gumf running & not much else when imaging, when i select 60fps sometimes it seems to drop a lot of frames ie when i watch the counter it will get to 10 secs & ill only have 400-500 frames not 600, this has happened imaging Jupiter & the other night trying Lunar, is this down to object brightness, optic size, 3x barlow in train too much for transparency or just me ?, i would have thought Lunar imaging would easily achieve 60fps & more so i am a little stumped.

I appreciate with Saturn it's position & brightness overall will effect what fps you can get & it makes sense to go low for fairly good seeing, is the imaging time about the same as Jupiter ?, Saturn - 10.5 hrs, Jupiter - 10 hrs ?

Appologies again Freddie but as i follow your's & Neil's work i thought you could both provide some answers.

Ewan

Sorry Neil i have just seen your reply on your thread i posted on re barlow, i have been slow in checking on replies :-(

Hi Ewan. Usually thre will be some frames droped depending on the specs of the computer, and how well kept the computer is, meaning if memory is low. or the pc cluttered with data. Heres things for you try, Let us know if any of it works. First clean the pc or lappy. meaning a general clean up delete ect. Next defrag the computer each and every time you image. Turn of programs you dont need. Turn off the net. disable anti virus and any other apllications you dont need while the net is going to be off.

Next when shooting at 60 fps, manually type into the EXPOUSE box ( on ic capture ) 1/61 secs exposure. this will force the camera to deliver full 60 fps. As there was a bug with software and this was a work around. Setting to 1/61 secs Exposure wont affect the exposure very much. as that increase in speed is quite minimal.

All this will still likely not deliver full 60 fps, it doesnt with me. but should certainly help the situation somewhat.

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Thanks for the comments guys, much appreciated.

That's a nice shot of Mars, not sure I will ever be brave enough to put my 4x and 2x together. I do shoot over the top of houses but they are not particularly close and being in a large village there are not that many of them. I'm in no doubt that the general conditions and seeing that morning played a big part in this image.

Neil, I'm not sure how well known this is but the IS cams have two internal modes of operation. I have no idea why. If you set the exposure shorter than the frame rate e.g. 1/40sec 30fps the cam takes the exposure and delivers to the computer to save in parallel. If you set the exposure to be longer than the frame rate e.g. 1/40 sec 60fps the cam takes the exposure then delivers to the computer to save in series. In this mode you obviously then end up with fewer frames than you would expect per second. If you match the exposure and frame rate e.g. 1/30sec 30fps the cam will operate in parallel mode, but you have to force it to switch by first setting a shorter exposure and then selecting the actual one you want. I must admit I sometimes forget this myself in the heat of the moment (or should that be cold!!!)

In terms of the exposure, you can only select the fixed options given by the cam but I always try and remember the above to maximise the number of frames being delivered to the laptop.

Ewan, there is not only the above to take into account but also check that your computer is not doing something else when you are capturing. Having security progs running or background checks can slow things down and limit the number of frames that end up being saved during a capture.

Hi again Freddie thanks for the discussion Its appreciated as no matter how much ive learned over the years, theres always something new to learn from other experianced imagers like yourself. And you certainly got my attention with this shot and settings used.

So just to clarify when you set the red to 1/13th secs exposure what frame rate setting did you choose. same question for blue at 1/9th secs. I am still unsure what you did. Sorry my brain is like fog recently.

Btw just as a aside. i think houses at some distance from the capturing site, are less of a problem than those much closer to the site. i am sure you agree.Others may find that info usefull. Unluckily mine are quite close. Which is less of a problem in spring than winter

Edited by neil phillips
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Hi Neil, yes I would agree that with houses further away it is not such a problem as any heat rise from them will have less of an impact as for any given object in the sky, the further away the house is, the higher above its roof you'll be aiming.

For the frame rate, I don't keep a record of that, only exposure. There are however two things to consider. 1. You will never get more frames per second delivered to your laptop than the frame rate you have selected. 2. You need to get the camera operating in the parallel capture and delivery mode rather than in the capture and delivery in sequence mode. As a demonstration of this, in live view set a 1/30 exposure and a frame rate of 60fps. The live view will show you are only getting ~20fps. This is because the cam is in series mode. Now change the frame rate to 30fps. You will now be getting 30fps as the cam will have changed mode to parallel mode. If you take these two things into acount you can set things up to achieve the maximum number of frames delivered to your laptop.

This can become a real pain if you want to set say a 1/45 exposure. Set 30fps and that's all that will be delivered (even though the cam can capture 45 per sec) Set 60fps and it puts the cam into series mode and you only get ~25fps. In this case, I find you are better off setting 1/60 exposure, 60fps and increasing the gain to get the histo you want. The increase in frame rate and therefore total number of frames captured allows you to overcome the greater noise you will have from the higher gain.

Hope all that makes sense.

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Hi Neil, yes I would agree that with houses further away it is not such a problem as any heat rise from them will have less of an impact as for any given object in the sky, the further away the house is, the higher above its roof you'll be aiming.

For the frame rate, I don't keep a record of that, only exposure. There are however two things to consider. 1. You will never get more frames per second delivered to your laptop than the frame rate you have selected. 2. You need to get the camera operating in the parallel capture and delivery mode rather than in the capture and delivery in sequence mode. As a demonstration of this, in live view set a 1/30 exposure and a frame rate of 60fps. The live view will show you are only getting ~20fps. This is because the cam is in series mode. Now change the frame rate to 30fps. You will now be getting 30fps as the cam will have changed mode to parallel mode. If you take these two things into acount you can set things up to achieve the maximum number of frames delivered to your laptop.

This can become a real pain if you want to set say a 1/45 exposure. Set 30fps and that's all that will be delivered (even though the cam can capture 45 per sec) Set 60fps and it puts the cam into series mode and you only get ~25fps. In this case, I find you are better off setting 1/60 exposure, 60fps and increasing the gain to get the histo you want. The increase in frame rate and therefore total number of frames captured allows you to overcome the greater noise you will have from the higher gain.

Hope all that makes sense.

Hi Freddie yes i am aware of this, its something i got to grips with long ago. It makes sense, which is why i am saying i dont understand at 1/13th secs how you got 9 fps. because you would have only two options 15 fps or 7 fps.

setting it to 15fps. I havent tested to see what frame rate that produces ? but would have thought lower than 7 fps for the reasons you just gave. But it cant be, because you say you got 9 fps

As mentioned i havent tested 1/13th secs exposure at 15fps. clearly if your saying you got 9fps at 1/13th secs exposure for the red, then really that would have been your only way to get it, the only other option is 7fps ? 1/3th secs exposure

I will test this out myself. . you only really had 1 option 1/13thsecs exposure 15fps. this must have been your settings Freddie.

if this is indeed so, its something i wouldnt have done, as you mention it must be set in parallel genearally. So of course this is something i didnt know. At 1/13th secs exposure i would have set the cam to 7 fps not 15. But you seem to have got more out of it in series mode as you put it. As clearly this is your only option of doing so, going above 7 fps at 1/13th secs exposure ? I will test 1/13 th secs expsure at 15 fps and see what happens. I didnt know this can be done

Edited by neil phillips
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Hi Neil, just done a test and got the following: 1/13 exposure, set fps 60=11fps, set fps 30=10fps, set fps 15=7fps, set fps 7.5=8fps. So looking at this I may have had the rate set at 30fps that morning (lucky accident, not intended!!). What's more interesting though is that setting the cam at the highest frame rate gives the highest output which is not what you would expect from the camera operating modes. The rule does appear to apply as expected at 1/15sec exposure and faster though. Wasn't expecting those results at 1/13 though. Interesting.

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Hi Neil, just done a test and got the following: 1/13 exposure, set fps 60=11fps, set fps 30=10fps, set fps 15=7fps, set fps 7.5=8fps. So looking at this I may have had the rate set at 30fps that morning (lucky accident, not intended!!). What's more interesting though is that setting the cam at the highest frame rate gives the highest output which is not what you would expect from the camera operating modes. The rule does appear to apply as expected at 1/15sec exposure and faster though. Wasn't expecting those results at 1/13 though. Interesting.

Hi Freddie wow that is interesting. something that really hadnt occured to me. To try 60 fps at that exposure.This conversation has been very fruitful indeed. Obviously if i had tried these slow exposures i would be losing 4fps if i had set it to 7 fps. Which is what i would have done before this converstaion. Makes sense Freddie if you was at 30fps, and dropped a few frames, hey presto your 9fps. I didnt realize these things occured quite like this either ( using 60fps at your exposure) which is why i said you was at 15fps.

I wonder if different spec lappys might behave differently Freddie. At some point i will do the same test to see what happens with a different lappy. Hmmm very interesting thanks for helping to clear this up, and discover the highest frame rate was at 60 fps. Some one needs to do a test on variouse exposures and fps settings to see what happens. though to be honest i think we should both be switching to firecapture, as i thought that could be set to the frame rate of the exposure. meaning 1/13th secs 13 fps If anyone knows. But i just love using IC capture. ive got used to it now, and will need a bit of time to get used to fire capture. Like i have ic capture.

old dogs and new tricks and such.

Cheers for the update Freddie. i was lost there for quite some time. It all makes perfect sense now doesnt it. Though still unsure why ic capture would behave like that.But who cares if you like the program, and want the most frames from it, Then heres what you do right here. Nice one

Edited by neil phillips
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Thanks for your comment Michael.

Question is, will we get good conditions again to have another go?

Things have been so bad lately. That is not a silly question at all Even though we have lots of time. it seems the uk weather is just bad bad bad. With weeks passing before one maybe night occurs. wheres the clear all night days on a run gone ? I reckon we will. as we enter spring. But its not a given is it

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Hi Neil, yes it goes against how IS say their cameras work. I have put this to Stefan over at IS. It's strange because at 1/15 sec exposures and faster, the cam does exactly what I would expect and how IS describe. It is only at the longer exposures that strange things happen.

On a 300 sec AVI, a few extra fps can make a real difference.

Edited by Freddie
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Hi Neil, yes it goes against how IS say their cameras work. I have put this to Stefan over at IS. It's strange because at 1/15 sec exposures and faster, the cam does exactly what I would expect and how IS describe. It is only at the longer exposures that strange things happen.

On a 300 sec AVI, a few extra fps can make a real difference.

Yeah it is weird. But its a good weird. Now im going to have to rethink my technique. Doing some tests to figure exactly what exposures do what. that or switching to fire capture. its just lazyness on my part.

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Hi Neil, I did a lot of different seetings this morning (you can save time from doing your own tests) and as I say, don't go slower than 1/15sec and the cam will do what you expect it to do. Slower than that and the camera mode rule doesn't appear to apply. So below 1/15 set the frame rate at 60. I don't think I've ever been slower than 1/15 before (it was misty that morning) so it was by accident that I've found this out. I should have just said I knew exactly what I was doing all along !!!!

I wouldn't have minded another few hunded frames each colour to play with, but the pic didn't turn out too bad anyway.

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Fascinating discovery Freddie! Just tested my DFK and its exactly as you say. It is annoying that frame rates higher than 30fps i.e 45fps cannot be achieved. I've tried Firecapture but can never get the full 60fps at 1/60 or 30fps at 1/30.

Looks like tonight could be a good one!

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Hi Stuart, with IC you should be able to capture at an actual rate of 60fps if you select that frame rate and set 1/60 sec exposure. What I find is that even if you think say a 1/45 sec exposure is ideally what you want, you will usually end up with better results if you set to 60fps, a 1/60 exposure and increase gain to compensate or just accept a lower histo than you would usually aim for. I'm often at 40%. The increase in the number of frames captured helps to control any added noise and the faster exposure really helps to freeze the moments of good seeing and capture as many frames as possible during those moments.

Hope you had a chance to get out tonight. Cloud, clouds and more clouds here!!!

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Yep I get 60fps ok in IC Capture Freddie, what I meant was its a shame by setting say 1/45 you can't get 45fps rather than 30fps.

Had planned to set alarm for Saturn but sitting up with a calving cow so looks like Saturn will have to wait for another night lol.

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