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Any good 5x barlows with M42 thread?


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Hi. I have a couple of 2x barlows that come with a M42 thread for direct connection to my DSLR via T-ring. They both work well enough when connected like this. I've noticed there are several cheap 5x barlows what also have the M42 thread - but none of the higher quality 5x barlows come threaded. Is there a reason for this as far as anybody knows? If not - are there any good 5x barlows that come with a M42 thread?

Thanks 

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Why would you need x5 barlow?

You can use x5 telecentric from ES or x5 Powermate from TeleVue together with 1.25"/T2 nose piece if you really need x5 amplification.

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19 minutes ago, vlaiv said:

Why would you need x5 barlow?

You can use x5 telecentric from ES or x5 Powermate from TeleVue together with 1.25"/T2 nose piece if you really need x5 amplification.

Thanks for the reply. I was talking about having an M42 thread at the eyecup end of the barlow. Basically, so it can sit between a refractor and a DSLR.

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47 minutes ago, soojooko said:

Basically, so it can sit between a refractor and a DSLR.

With x5 barlow you are very likely to be over sampling.

What do you want to image? What is refractor F/ratio and what is pixel size of your DSLR?

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21 minutes ago, Louis D said:

Is there a reason you're averse to using a 1.25" to T2 nosepiece adapter?  There's one one ebay UK for £7.99+S/H:

Are you super concerned about edge vignetting or image train tip/tilt/sag to want it integrated into the Barlow?

I already have one of those adapters. Again, I was talking about having an M42 thread at the eyecup end of the barlow, not the barrel end. For example, see here:

 719zL8E9kLL._AC_SY606_.jpg

You can see the M24 thread at the eyecup end. I was just wondering why there are no 5x barlows with this thread.

3 minutes ago, vlaiv said:

With x5 barlow you are very likely to be over sampling.

What do you want to image? What is refractor F/ratio and what is pixel size of your DSLR?

I don't have the gear yet. Just figuring things out. I already have an imaging setup, with a DSLR and some lens. Im considering a small refractor: 50-60mm aperture with a focal length of around 250-350. I was checking out the different FOV when using barlows and was curious if a 5x could work. But without the M42 thread, its not possible as far as I can see.

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1 minute ago, soojooko said:

But without the M42 thread, its not possible as far as I can see.

It is possible and fairly simple - use 1.25" / T2 extension (you can do that with any 1.25" barlow.

Although you can achieve any FOV that way - it is not possible to get detailed image at any FOV.

With x5 barlow and F/6 scope - you'll be operating at F/30 - you will get very blurry image that way without much detail.

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Just to be very clear - this is setup that goes into a 1.25" barlow:

image.png.17f59adbec520b7e1a85d85e456ac117.png

It is T2 ring for DSLR + 1.25" / T2 nose piece screwed in - you can insert this into a barlow like any other 1.25" eyepiece.

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7 minutes ago, vlaiv said:

It is possible and fairly simple - use 1.25" / T2 extension (you can do that with any 1.25" barlow.

This has been suggested a few times but I didnt understand. Its only just clicked what you guys are saying! Yes - it is quite simple. And yes - I had a massive Doh! moment.

I appreciate that 5x might be a bit extreme. I wanted to get an idea of the extreme ends of magnification. Would you say that it is similarly impractical to use a high-ish powered eyepiece ( 8mm ) and do eyepiece projection? 

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22 minutes ago, soojooko said:

I appreciate that 5x might be a bit extreme. I wanted to get an idea of the extreme ends of magnification. Would you say that it is similarly impractical to use a high-ish powered eyepiece ( 8mm ) and do eyepiece projection?

That really depends on what you are trying to image.

If you are trying to image the Moon or planets - then there is certain F/ratio that depends on pixel size. This is only feasible if you are using lucky imaging technique by shooting very large number of images that are very short in exposure (up to 5ms). Some DSLRs are capable of doing this in video mode - but not all (because they use compression for video and that causes artifacts).

It is better to use dedicated planetary camera to shoot these kinds of images.

If you want to shoot deep sky objects - then in general - you don't need to use barlow, Even x2 barlow will be too much magnification because atmosphere blurs the detail.

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Posted (edited)
26 minutes ago, vlaiv said:

That really depends on what you are trying to image.

If you are trying to image the Moon or planets - then there is certain F/ratio that depends on pixel size. This is only feasible if you are using lucky imaging technique by shooting very large number of images that are very short in exposure (up to 5ms). Some DSLRs are capable of doing this in video mode - but not all (because they use compression for video and that causes artifacts).

It is better to use dedicated planetary camera to shoot these kinds of images.

If you want to shoot deep sky objects - then in general - you don't need to use barlow, Even x2 barlow will be too much magnification because atmosphere blurs the detail.

To be honest, ive no real interest in planets. Im a DSO type person. However, im finding myself wanting to ( attempt to ) image some of the smaller DSO, such as the whirlpool or sunflower galaxies. I don't really have the money to invest in a new rig. I'm currently using a Star Adventurer, so I can only use a small refractor. But I understand that making my scope really slow wont help me as I'll need to take absurdly long subs. Maybe its just not possible without moving to a bigger mount and telescope?

Edited by soojooko
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16 minutes ago, soojooko said:

To be honest, ive no real interest in planets. Im a DSO type person. However, im finding myself wanting to ( attempt to ) image some of the smaller DSO, such as the whirlpool or sunflower galaxies. I don't really have the money to invest in a new rig. I'm currently using a Star Adventurer, so I can only use a small refractor. Maybe its just not possible without moving to a bigger mount and telescope?

Ok, I see.

Here is the thing - you can only achieve so much with given aperture. Small scope - 50-60mm one, will simply resolve less than 100mm one - even with seeing involved.

This does not mean you can't image smaller galaxies - it just means that you need to understand that there will be limit to what you can resolve - or how "close in" you can get.

Part of getting in close - is FOV. You can adjust FOV by cropping your image. As long as you don't try to enlarge your image past what you can resolve (and get just blurry result) - you will be fine.

To give you some idea - let's take few smaller galaxies and see what sort of size they have:

M51 is 11 arc minutes x 7 arc minutes. That is 660 x 420 arc seconds.

M63 is similar in size

So is M94

To this size - you need to apply your sampling rate - one that you can achieve with such small telescope - and that would be 3"/px.

Galaxy size that you can resolve will be around 200-300px across. This is your target size. In order to fit galaxy into FOV - you should really crop to about 1000px to 1200px max in width.

Here is M51 in FOV that you would get if you crop your image to 1000px and sample at ~3"/px

image.png.7d2c61bebc31b6a9a531234b1fb63cb2.png

(Fov is whole gray background - not just part in the center - I simply did not have large enough M51 image to make example.

You can't zoom in further into such image - it is as large as it is - only 1000px across. But it will look nice.

 

 

 

 

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10 minutes ago, vlaiv said:

Ok, I see...

That's some great info there. Thank you so much. I never really considered what you are saying: cropping my image from 5000px wide to 1000px gives me the same FOV as using a 5x barlow - except without slowing down the scope. I think I can live with sacrificing resolution to get brighter subs.

 

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