Budget-ish Barlow recommendations for 130mm triplet?

[AndyThilo]

Hi

Anyone have any recommendations for a reasonable Barlow that would work ok with a 130mm triplet, FL 920mm? Also how much does it affect imaging sensor focal position?

Thanks

Andy

[vlaiv]

What will it be for?

Barlow lens tend to push focus position further out - something easily handled with extension tube.

If it is for imaging - question is, what sort of imaging, or rather what sensor will you be using (size) and for what purpose. With planetary imaging - any barlow will really do.

If you want to cover the whole sensor - then you need to think sensor size - not many barlows will cover APS-C sized sensor - at least not those in 1.25" format.

For regular barlow / planetary use, I guess this will be sensible budget option:

https://www.firstlightoptics.com/barlows/bst-starguider-2x-short-barlow-lens.html

do bare in mind that sensor/barlow distance determines magnification factor.

Telecentric lens don't significantly change the focal point nor do they significantly change magnification with sensor distance. I've heard that these are very good value for the money:

https://www.firstlightoptics.com/barlows/explore-scientific-2x-3x-5x-barlow-focal-extender-125.html

and they also come in 2" version - which would be good for larger sensor:

https://www.firstlightoptics.com/barlows/explore-scientific-2x-barlow-focal-extender-2.html

[AndyThilo]

Thanks for your comprehensive response. I’d be using my QHY5III462 so a nice small chip for planetary. 
 

Not in a huge rush as I’ve lost Saturn and Jupiter for the year but Mars is still quite high. 

[vlaiv]

If planetary is your main objective - I would suggest that you calculate how much barlowing you need in the first place, and then decide based on that.

Your camera has 2.9µm pixel size and optimum focal length for 130mm aperture and mono camera is around 1479mm

Since your camera is color - double that for 2957.28 mm. If your focal length is 920mm then you really want x3.2 barlow. Go with x3 barlow / telecentric lens. After processing, just reduce image back x2 in size to return to optimum sampling rate if you want your images to be sharp.

Alternative is to use x1.5 barlow and then to bayer drizzle - but not sure if that is still available in AS!3 (option to use it was gone last time I checked and I don't know if it is now default mode for debayering or something).

[AndyThilo]

Thanks I was thinking a 3X, now the issue is finding one lol, no one has any  

3X produces a reasonable FOV for the planets and should be nice and close for moon shots. 

[Merlin66]

The ES x3 tele-extender is a reasonable option, it’s very close to being a telecentric, like the TV powermates.

I use one on the SM60/ ED80 for solar observing when the seeing is good.