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Old 01-02-2013, 11:51 AM
04Stefan07 (Stefan)
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What Barlow to use with a 5" scope (to capture outer planets)?

I currently have a 2x Barlow and tried it out on Saturn the other morning. I was able to capture Saturn but it was quite small and had no detail on it. I had to increase the exposure and gain a bit.

I know a 3x Barlow would increase the size of the planets but would I be able to capture enough light with my scope using a higher magnification? Would I even be able to get away with a 5x Barlow?

Thanks.
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Old 01-02-2013, 06:10 PM
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wasyoungonce (Brendan)
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Stefan, it doesn't matter what barlow you are using you are still gathering the same amount of light...however...you are spreading this amount over a greater image circle with that barlow. Thus the image will be increasingly dimmer as you go up in barlow magnification.

At a certain point it's no use magnifying any more as the image is getting real dim. Many users have done very well with 5X powermates but I suspect they are using these on big reflectors of short'ish FL's, F4 etc.

If you are using the 130slt that's an F5 so 3X is F15, 5X is F25. Imaging @F25 is achievable but I think you would be limited but the size of the optics. I have imaged at F30 with a C8 but it is demanding of the equipment, shakes, atmospheric disturbances etc. There are probably few times it could be used due to atmospherics.

Given the cost of a 5X powermate.....I suspect it will be a loss exercise to go higher in magnification unless you are gathering more light. Anyway FWIW?

edit:
Oh I should have said I went from a 2X barlow to a 3X and was disappointed in the limited change and dim image.
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Old 02-02-2013, 05:19 PM
04Stefan07 (Stefan)
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Quote:
Originally Posted by wasyoungonce View Post
Stefan, it doesn't matter what barlow you are using you are still gathering the same amount of light...however...you are spreading this amount over a greater image circle with that barlow. Thus the image will be increasingly dimmer as you go up in barlow magnification.

At a certain point it's no use magnifying any more as the image is getting real dim. Many users have done very well with 5X powermates but I suspect they are using these on big reflectors of short'ish FL's, F4 etc.

If you are using the 130slt that's an F5 so 3X is F15, 5X is F25. Imaging @F25 is achievable but I think you would be limited but the size of the optics. I have imaged at F30 with a C8 but it is demanding of the equipment, shakes, atmospheric disturbances etc. There are probably few times it could be used due to atmospherics.

Given the cost of a 5X powermate.....I suspect it will be a loss exercise to go higher in magnification unless you are gathering more light. Anyway FWIW?

edit:
Oh I should have said I went from a 2X barlow to a 3X and was disappointed in the limited change and dim image.
OK cool thanks for the advice
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Old 02-02-2013, 06:12 PM
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PRejto (Peter)
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I agree with previous comments. I have had very good results from the Televue 3X Powermate with my TEC140. I have seen excellent images with the TEC140 and the 5X Powermate so I invested in one only to find that I was normally defeated by the atmosphere and I consistently obtained better results with the 3X. But, it isn't only atmosphere. As the image gets dimmer you will find that you cannot capture at a high enough frame rate, and that is not a small consideration. I think on a good steady night, on Jupiter, the 5X would possibly get me good results, but with Saturn, and a 5" scope it is probably not going to make you happy, at least very often. If you get excellent focus, steady air, fast frame rate, and a long enough capture, you will be surprised at what you can get. In my view 3X on a 5" f21 or so would be the way to go. Later I will attach 2 images that I took a year or two ago with the TEC140, one at F35 of Saturn on a lucky night (for me).

Edit. I just realised your scope is f5. So, what you get with a 3X is close to what I would get at f7 and a 2X barlow. Perhaps you would be ok with a 4X barlow putting you at f20...this would be very close to what I have imaged at, though the TEC140 has near perfect optics with no obstructions and an extra .5" Still, on a good steady night it might get you a very good result.

Oh, you did not say if you were capturing with a mono or colour camera. I know most serious planet photographers go for mono; I would say your problems are increased 3 fold, but for an appreciable gain. Having said that, however, perhaps cut your teeth so to speak with a decent colour camera as you will probably get a better result sooner and not get too discouraged! (The photos I posted are from a colour camera)

Edit #2: You can also experiment with your existing 2X barlow. Just get an extension tube and increase the distance from the barlow to your CCD. You may get 3X or more depending on the distance and still have pretty good quality. There are ways to calculate the exact power. Shouldn't be hard to locate the formula.
Attached Thumbnails
Click for full-size image (Saturn - video0024 - final.jpg)
42.5 KB62 views
Click for full-size image (Jupiter - 214128 - combined_RGB-combined-LRD-color adj-final.png)
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Last edited by PRejto; 02-02-2013 at 10:45 PM.
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Old 03-02-2013, 12:34 AM
04Stefan07 (Stefan)
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I am using a colour camera. I have posted a photo of Saturn in the beginners astrophotography section if you want to have a look at what I got using a 2x barlow.

Your images look fantastic! Great detail is show.

So you think it's better to get an extension tube or a 3x barlow? I don't want to end up spending on a 5x if the results won't be that great plus it would be much harder to use at the higher magnification.
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Old 03-02-2013, 08:37 AM
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I would say your least expensive option is to try an extension tube on your 2X barlow. See how that works out first.

I don't recommend a 5X barlow, but perhaps a 3X with a bit of extension would get you to 4X and f20. I think that is a reasonable image scale vs average seeing.

I'll try to find your photo!

Tell me, how are you focusing? What frame rate are you able to capture at, and finally, what software are you processing with?
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Old 03-02-2013, 01:34 PM
04Stefan07 (Stefan)
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Quote:
Originally Posted by PRejto View Post
I would say your least expensive option is to try an extension tube on your 2X barlow. See how that works out first.

I don't recommend a 5X barlow, but perhaps a 3X with a bit of extension would get you to 4X and f20. I think that is a reasonable image scale vs average seeing.

I'll try to find your photo!

Tell me, how are you focusing? What frame rate are you able to capture at, and finally, what software are you processing with?
Here is the thread.

http://www.iceinspace.com.au/forum/s...d.php?t=102763

Depending on the resolution I can capture frame rates between 50 and 5 FPS. I am focusing manually using the focusing knobs on the scope itself. I am using Celestron's iCap software but also have SharpCap software installed to experiment with.
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Old 04-02-2013, 09:48 AM
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I have not used any of those software solutions, but generally you must set various parameters to give you the best looking image before you capture anything.

If there is a histogram in the capture software use it! Make totally sure that nothing is clipped. Usually I just increase gain to around 70% and make sure that all three colours are balanced and none are clipping. The colour needs to look as natural on your screen before capture as you can get it.

Focusing is massively critical and hard to get and maintain. You might consider using a mask of some sort, even slewing to a nearby star to focus. Your scope is fast so the critical focus distance is extremely small, but you have got to nail it.

Capture at the highest frame rate possible, but not so high as to introduce noise from gain. You can see this noise when the image starts to
Look grainy. You need to capture are many frames as possible! You did not say how long you are capturing. At 30 fps one min will give you 1800. You can capture for 2 to 3min....

Try using Autostakkert to process your video. It is fast and quite good! You should see a fairly good result coming out of Autostakkert....if not probably all the processing in the world will not rescue the image. But, if you have a good result it is amazing what you can pull out. There are zillion tutorials on planetary processing so I will stop here.

Looking forward to seeing your next efforts. You can get a surprising amount out of 5"

Peter
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Old 04-02-2013, 01:14 PM
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jjjnettie (Jeanette)
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I tried out my 4x Powermate on my 5" Refractor and was pretty pleased with the results.
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Old 04-02-2013, 02:53 PM
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mithrandir (Andrew)
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Quote:
Originally Posted by jjjnettie View Post
I tried out my 4x Powermate on my 5" Refractor and was pretty pleased with the results.
I must try that - if the sky ever clears and at the same time the wind drops below gale force and the temperature below 40.
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  #11  
Old 04-02-2013, 03:37 PM
04Stefan07 (Stefan)
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Quote:
Originally Posted by PRejto View Post
I have not used any of those software solutions, but generally you must set various parameters to give you the best looking image before you capture anything.

If there is a histogram in the capture software use it! Make totally sure that nothing is clipped. Usually I just increase gain to around 70% and make sure that all three colours are balanced and none are clipping. The colour needs to look as natural on your screen before capture as you can get it.

Focusing is massively critical and hard to get and maintain. You might consider using a mask of some sort, even slewing to a nearby star to focus. Your scope is fast so the critical focus distance is extremely small, but you have got to nail it.

Capture at the highest frame rate possible, but not so high as to introduce noise from gain. You can see this noise when the image starts to
Look grainy. You need to capture are many frames as possible! You did not say how long you are capturing. At 30 fps one min will give you 1800. You can capture for 2 to 3min....

Try using Autostakkert to process your video. It is fast and quite good! You should see a fairly good result coming out of Autostakkert....if not probably all the processing in the world will not rescue the image. But, if you have a good result it is amazing what you can pull out. There are zillion tutorials on planetary processing so I will stop here.

Looking forward to seeing your next efforts. You can get a surprising amount out of 5"

Peter
That's really good advice, thank you.

By the way how does an extension bump up a 2x Barlow to a 3x? I am actually going to Bintel tomorrow so would I be able to get this?

http://www.bintel.com.au/Accessories...oductview.aspx
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  #12  
Old 05-02-2013, 09:43 AM
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PRejto (Peter)
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Here: http://en.wikipedia.org/wiki/Barlow_lens

And http://w1.411.telia.com/~u41105032/barlow/Barlext.htm
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Old 05-02-2013, 12:42 PM
04Stefan07 (Stefan)
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Cool thanks ill have a read.

Might as well grab that extension tube from Bintel!
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Old 06-02-2013, 04:35 PM
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Shiraz (Ray)
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depends entirely on the pixel size of the camera and the F Number of the scope.

easy rule of thumb is that the final F Number you obtain should be roughly equal to the camera pixel size in microns multiplied by 5.

For example if you have a camera with 3 micron pixels, you want around f15 - so if you have for example an f8 scope, you will get close to f15 with a 2x Barlow or if you have an f5 scope, 3x would be best. I have an f5 scope and 5.6 micron pixels, so I need about f28 and use a 5x Barlow.

this method optimises things for both the scope aperture and focal length - you only need to consider the pixel size and final f number and everything else falls into place.

Last edited by Shiraz; 06-02-2013 at 06:37 PM.
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Old 06-02-2013, 07:12 PM
04Stefan07 (Stefan)
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Quote:
Originally Posted by Shiraz View Post
depends entirely on the pixel size of the camera and the F Number of the scope.

easy rule of thumb is that the final F Number you obtain should be roughly equal to the camera pixel size in microns multiplied by 5.

For example if you have a camera with 3 micron pixels, you want around f15 - so if you have for example an f8 scope, you will get close to f15 with a 2x Barlow or if you have an f5 scope, 3x would be best. I have an f5 scope and 5.6 micron pixels, so I need about f28 and use a 5x Barlow.

this method optimises things for both the scope aperture and focal length - you only need to consider the pixel size and final f number and everything else falls into place.
Yep thank you!
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Old 18-05-2013, 11:09 AM
Skrae (Lex)
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Cheers!

Just stumbling around looking at various posts and I found this.

Been using my barlow wrong all this time! I have a 130slt on a Skywatcher EQ5 GOTO mount, Add the 50d on to that and the focuser on the slt seems to have too much of a wobble so I ended up removing the barlow from its tube and attaching it directly to my tring and slotting a 9mm just inside (it barely clears the cameras mirror. freaked out the first time i took a photo...)

Might need to re assess how things are going...
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