Is it 'wrong' to use a Barlow lens with a camera

[Fishpaste]

I'll come clean - I don't have a telescope yet, or mount (but I hope to soon)... just using DSLR and tripod at the moment...
I've read a few times that you shouldn't use a Barlow lens when photographing.. is this correct? Is it just because it slows down the setup (ie increases focal length) -- or is there another reason for it...?

Only I would rather not have to buy a second scope if I wanted to do some close up pics of the moon or something!

...or am I being thick and missunderstood?

[Leveye]

A Barlow is made for use with an eyepiece and telescope focuser tube either 2' or 1.25'. You can use a camera like a P nS or webcam afocal thru the eyepiece with an adaptor. I have seen adaptors for attaching a DSLR to the telescope with an eyepiece and Barlow inserted but not anything using one with a full DSLR and a camera lens with a barlow.

[Tel]

You can only use a Barlow with a telescope, if you want to increase the magnification use a tele extender for your lens they come in 1.5 or 2x as standard so your 300mm will become a 450 or 600mm lens. It will however slow your shutter speed down compensate by increasing the iso.

[Cath]

No, it's not wrong Fishpaste .. on a telescope with camera that is.

[Fishpaste]

ahh... I see Leveye - so once I have chosen my telescope (SW ED80 Pro I'm considering).... when doing prime focus photography, there is no way to 'zoom in' (increase magnification) on objects... the only way is to blow it up in Photoshop later? is that correct?

[Fishpaste]

Hmmm.. I think my original post (and title) weren't very clear... I was (obviously) not intending to stick a barlow lens on a camera.. I basically meant was it ok (or not) to put a Barlow on a telescope when doing prime focus AP...

 

[LouisJB]

you can but it slows down your setup so for example with a 2x barlow you might need twice as long exposures. In a world of perfect guiding etc (and unlimited time) then this wouldn't matter, but in practice it often does, a lot.

However, for the Moon (or Sun, with suitable filters) these targets are so bright that a barlow is a possibility. Of course you might get CA with extra glass in the optical path.

For DSOs etc you really want nothing in the path other than a coma corrector for a Newt (or equivalent flattener for a refractor)

[Uranium235]

I'll have to take a different line and say a barlow should never enter the optical train unless you are doing lunar, planets or visual.

First reason being it will introduce shedloads of coma or star distortion and the useable field will be quite small. Second reason is it will more than quadruple your imaging time.

Example:

A 2x barlow in an 80ED will take it to f14.

f14 is 4.81x slower than the same telescope with the 0.85x reducer (f6.38)

Stick to prime focus and use either a coma corrector (if using a newt), or a reducer/flattener (if using a refractor).

[ollypenrice]

Hmmm.. I think my original post (and title) weren't very clear... I was (obviously) not intending to stick a barlow lens on a camera.. I basically meant was it ok (or not) to put a Barlow on a telescope when doing prime focus AP...

99.9% of the time it is emphatically not OK. DS imaging is usually about collecting faint data across the chip and for this you need a fast F ratio. A 2x Barlow would slow you down by 4X. (DS imaging is already slow. Don't multiply slow by four!!) The planetary guys and gals can do it because planets are bright. Faint dust and gas isn't.

If you want to fill the frame with small targets you need more focal length and more aperture. More focal length without more aperture is no good.

We've seen literally a couple or three good DS images on here done through Barlows. A fast scope and a Barlow on a bright target is not out of the question but it is a once or twice in a lifetime kind of thing.

Olly http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/22435624_WLMPTM#!i=2266922474&k=Sc3kgzc

[Killie]

I think this has pretty much been said but I do use a Barlow for webcam photography of planets and the moon etc. but I don't think I would go near it with DSO. In fact with my set up I would more likely use a reducer.

[LouisJB]

yeah that's a good way to put it - in AP most times people require a reducer to speed things up, not a barlow to slow things down!

[Fishpaste]

so - in short.. whatever telescope you buy, for deep sky object photography the 'magnification' is pretty much non-negotiable.. it is what it is... and if you want anything different you will need another telescope!

[Tiny Small]

You can use a barlow. It makes things a bit slower but yes you can. Skywatcher barlows come with a T thread to attach to a DSLR and the glass element of the barlow is removable, so you can either use it as a nose piece or as a barlow. Not ideal but if you can't afford lots of scopes, it is an option. Without perfect tracking you will struggle to get massively long exposures but hey... you make do. Having looked through Olly's photos, he knows exactly what he is on about, but I have also looked at his website and seen what kit he has. Those budgets are simply out of the question for most people, so with patience and practice, never say never.

[Tiny Small]

Having said that, you don't need a lot of focal length for most stuff... because they're pretty big once you get a long exposure going.

[ollypenrice]

You can use a barlow. It makes things a bit slower but yes you can. Skywatcher barlows come with a T thread to attach to a DSLR and the glass element of the barlow is removable, so you can either use it as a nose piece or as a barlow. Not ideal but if you can't afford lots of scopes, it is an option. Without perfect tracking you will struggle to get massively long exposures but hey... you make do. Having looked through Olly's photos, he knows exactly what he is on about, but I have also looked at his website and seen what kit he has. Those budgets are simply out of the question for most people, so with patience and practice, never say never.

As a professional provider I can get expensive kit past my conscience but an HEQ5 with ED80 and Atik 314L or 383 CCD would probably get closer than you think, in all honesty. The big difference would just be in field of view.

so - in short.. whatever telescope you buy, for deep sky object photography the 'magnification' is pretty much non-negotiable.. it is what it is... and if you want anything different you will need another telescope!

Yes, that's about it. It's best to avoid the term magnification but since you put it in inverted commas I can see that you know this. The image scale (size of the object on the chip) is determined by the focal length of the system and nothing else. Photographers have assorted lenses. Imagers have assorted scopes, very often. One or two very high end astrographs have highly variable focal lengths and enough aperture to suppport a reasonable F ratio at the longer end. It's usually cheaper to buy two other scopes!

Olly

[Chris Rowland]

I wouldn't hesitate to put any sort of secondary optics on a scope/camera combination to get the results I want,  a focal reducer for DSOs if I want a wider field or a Barlow if I want more magnification for planets and the Moon.

A F/10 SCT with a x2 Barlow to give F/20 isn't at all unusual for the moon and planets, some use a x3 Barlow to give F/30.  Christopher Go uses a C14 with a x2.5 Barlow to get superb images of Jupiter.

Chris

[Langy]

This may be a stupid question, but does it not matter what type of telescope you use the DSLR on?

For example I have the Astromaster 130EQ Reflector, if I take out the EP and use either a DSLR or WebCam straight in the EP there is only one distance within the EP holder where you can focus the image. In order to change that by either reducing or increasing the image size you have to have some form of a lens fitted first before the camera. I don't know how the tele extenders work as mentioned before, but they must have some form of a lens in them to extend the focal length of the scope. As with all photography when you introduce extra elements like a piece of glass or increase the focal length you lose the intensity of light therefore making exposure times longer.

I wait to be corrected.

[jgs001]

Can you use a barlow for deep sky imaging... yes you can. I've done so... but... with a 2x barlow, you double the focal length, and therefore the focal ratio, which has the effect of needing four times longer to capture the same amount of data. Is this practical... not really, even with an excellent guiding setup, a dSLR heats up the longer you expose each frame for, and this causes heat and noise in the image. You can capture 4x as many exposures at half the image scale, and then crop in etc as needed in processing.

For testing my guiding, I add a barlow into my ED80 and shoot a single 20 minute exposure, but then at that point, I'm not really bothered about the result, I'm looking to make sure my stars are round.

[LouisJB]

so in short, yes you can use one. In particular the OP said:

"Only I would rather not have to buy a second scope if I wanted to do some close up pics of the moon or something!"

and because the Moon is so bright this really is a place where a barlow can be used perfectly. In particular the Moon, planets and Sun (with suitable filters!) are ideal for barlowing. For example unless you have a high focal length SCT or similar most planets will be pretty small and a barlow in conjunction with a web cam will help scale the image up a bit.

For anything DSO related, you could give it a go, but if you're turning your 5 minute exposures into 20 minute exposures you may have far more problems to worry about than the image scale.

Best thing is get one and experiment, a barlow is always useful in the kit, you'll use it on the Moon and planets. For DSO what you might want more importantly is a coma corrector.

[michael.h.f.wilkinson]

As the OP states, he wants to zoom in on planets and the moon. A Barlow is fine for that. It should not introduce coma and the like, or have a tiny usable FOV. DSLRs are of course not ideal for planets, but I got some really nice lunar shots with a 2.5x PowerMate and my EOS 450D

[LouisJB]

exactly, for example I've just got a 5x barlow for next attempts at Jupiter/Saturn with video where previously I was using a 2x - so they have their uses. I'd definitely barlow the Moon if I wanted to get in close and see detail on a part of it.

Coma correctors are for correcting the edges of a wide-field, you'd not use the two together, two different things.

[Langy]

I did use my EOS 300D with 2x Barlow on the moon last night. But with the thin cloud cover was unable to get anything useful. Even on my scope it filled the frame and exposure times were already getting down to 1/20, but without the cloud I suspect that with speed up.

[RT65CB-SWL]

Hi Fishpaste,

I would say give it a try. Should be OK for lunar close-up & solar (filtered) for close-ups of sunspots and the major planets, but not for DSO's. From what I have read they are perfect with a webcam.

A Barlow lens seems to have the same effect as a 'matched multiplier' for a camera lens, ie everything doubles or trebles in value and apature is divided by two or three. I tried several years ago on Jupiter and Saturn with a 35mm film SLR. The result was a 'bit' grainy.

TeleVue do a 'PowerMate'. These are slightly different to a 'conventional' Barlow lens, but I believe same principle. However dearer than a Barlow too! I think somewhere on the web, (may have been on the TeleVue site), someone explained the differences.

[RT65CB-SWL]

Hi Fishpaste,

I would give it a try. Should be OK for lunar close-up & solar* for close-ups of sunspots and the major planets, but not for DSO's. From what I have read they are perfect with a webcam.

A Barlow lens seems to have the same effect as a 'matched multiplier' for a camera lens, ie everything doubles or trebles in value and apature is divided by two or three. I tried several years ago on Jupiter and Saturn with a 35mm film SLR. The result was a 'bit' grainy with 100ASA.

TeleVue do a 'PowerMate'. These are slightly different to a 'conventional' Barlow lens, but I believe same principle. However dearer than a Barlow too! I think somewhere on the internet, (may have been on the TeleVue website), someone explained the differences.

* Remember that a solar filter must cover the full aperture of your 'scope and your finder and/or red dot finder. DO NOT and I repeat DO NOT use a solar filter that screws into an eyepiece.

[Tiny Small]

A Barlow lens seems to have the same effect as a 'matched multiplier' for a camera lens, ie everything doubles or trebles in value and apature is divided by two or three.

It's knowing how to apply the Inverse square law. If you are looking at a light source with the naked eye and you then double the distance you get the square root of the light, likewise if you half the distance you get its square (4x in this case as you halved the distance). Where optics are concerned its exactly the opposite. if you double the focal length (by use of a 2x barlow for example, which is analogous to halving the distance), you get the square root of light where as if you half the focal length (analogous to doubling the distance), you get its square. Getting your starting lights root may only be a small reduction where as getting its square is a massive step up, for example, the root of 9 is 3, where as the square of 9 is 81.