Which barlow with a 5" scope ?

[Kakadush]

Hello all  

So i recently started doing planetary imaging with my ASI 120 + 5" Celestron 130 slt scope and i'm pretty happy with my progress however , i find that the size of the planets i capture is rather small (see attached image for reference) and i was wondering if using a higher power barlow would do any good.

Right now i am using a x2 barlow and i was thinking of getting a x3 or even a x4 but from what a gathered because my scope is rather small i might have problem focusing with higher power barlows , my questions are : 

*Will a higher power barlow incrase planet size and reveal more detail or will it be simply larger and blurry ? 

*Will it affect image resolution in any way ? 

*If not , should i get a x3 or x4 barlow ? 

The scopes mirror is 5" , the focal length is 650mm and the aperture is 130 mm (reflector).

I am new to this so any help would be much appreciated , thank you !  

Dan.

[damnut]

Hi Dan,

If you took that image that's a great shot,  your scope's theoretical limit is 260x. That might be in nirvana but realistically c160 -200x will be your maximum.

Below a couple of pages to show you what you can expect to see. Just plug your scope data and eyepieces in and they do the work!

http://www.stargazing.net/naa/scopemath.htm

http://www.12dstring.me.uk/fov.htm         (remember to switch to visual view)

[JamesF]

I see no reason that you couldn't go up to 4x if the image is bright enough, and I've certainly had quite acceptable results with the ASI120 at that kind of focal length with similar apertures.

What I might be tempted to do is to get the Revelation Astro 2.5x barlow which is very good considering that it's only about £40 and then experiment with different length extensions between the barlow and camera to increase the power.

The large-ish sensor of the 120 helps a little, but if you have no barlow and get the planet centred and then bang in a 4x barlow you may find that it's a real pain to find the target again.

James

[Kakadush]

Hello all

So i recently started doing planetary imaging with my ASI 120 + 5" Celestron 130 slt scope and i'm pretty happy with my progress however , i find that the size of the planets i capture is rather small (see attached image for reference) and i was wondering if using a higher power barlow would do any good.

Right now i am using a x2 barlow and i was thinking of getting a x3 or even a x4 but from what a gathered because my scope is rather small i might have problem focusing with higher power barlows , my questions are : 

*Will a higher power barlow incrase planet size and reveal more detail or will it be simply larger and blurry ? 

*Will it affect image resolution in any way ? 

*If not , should i get a x3 or x4 barlow ? 

The scopes mirror is 5" , the focal length is 650mm and the aperture is 130 mm (reflector).

I am new to this so any help would be much appreciated , thank you !

Dan.

Thanks James , Damian !

Damian those are great tools , from what i gather i can go up to f/20 with my scope which is what a x4 barlow will give me , that said , am i being optimistic thinking i will be able to effectively use my scope's full power considering i live in a light polluted area with mostly average seeing ? 

And thanks for the image feedback , that is indeed my shot  

[JamesF]

There's no reason you shouldn't be able to do some pretty good planetary imaging from a light-polluted area.  As long as you're able to find the target it's worth having a go.  The quality of the seeing is just how it goes really.  You'll get good days and bad days.

James

[Kakadush]

I have heard some people put 2 x2 barlows instead of using a single x4 barlow , is a viable option or will i get better results with a single x4 barlow ? 

Dan

[damnut]

If you have achieved that image of jupiter you are way on the right path!! Using more magnification isn't going to bring the image that much closer (jupiter is a long way away) but will darken your image and as James says will make finding it a pain. You may have guessed I am not a fan of barlows., though I do own one it's not been out of its box

[JamesF]

I think you're more likely to get better results with a single barlow than by doubling them up.  In another recent thread where a poster had put two barlows together it didn't look like they were achieving anything like the increase in power they were expecting because the lens units need to be a specific distance apart to get the full effect.  (I can't recall the exact details off the top of my head, but the actual effect they were achieving was considerably less than what was expected given the powers of the barlows.)

I think going for the 2.5x barlow with extension is a better plan all round though.  A 40mm-ish extension would probably get you to somewhere around 3.3x (I used to use an old Skywatcher kit barlow that i'd removed the lenses from as an extension, as the barlow wasn't exactly brilliant to start with).  Also, there aren't too many 4x barlows about.  There's an ImageMate 4x, but a lot of people have struggled with it and I'm really not sure it's up to the job.  The 4x Powermate is both expensive and requires a 2" focuser.  If you then get to the point where the planetary imaging bug has bitten hard and you want to do even better, a different OTA may be the biggest improvement you could make.

James

[Kakadush]

Sorry for the late replay , James i didn't actually know about tube extenders , after reading your advice i began attaching a T-adapter i had laying around to my barlow as an extender and it works great so thanks again for the info ! 
I also ordered a x3 barlow that should work nicely with the extension
i'll post the results , cheers ! 

Dan.