Jump to content

290128050_ConstellationBanner.jpg.6eb5d1fe82e0853d4c3b80a745d12d74.jpg

2x BST and 3x Xcel-lx focal point


Recommended Posts

Hi all

Very niche question here. I’ve been imaging with a 2x BST shorty barlow but have the option to buy a used 3x Xcel-lx to get to optimal f-ratio. Currently my 2x + camera focuses very very close to the bottom of the focuser, so I’m wondering whether the 3x will push the focal point backwards or forward. I understand that this may depend on the barlows in question so have included them in the title, but if it’s just a matter between 2x and 3x even better! 

TIA

Ross

p.s. I’ve put this in eyepieces rather than imaging because I would imagine more people browsing the eyepiece and barlow topic would have experience with the two focal points than in the imaging topics.

Link to comment
Share on other sites

Hi Ross, I know your predicament from your other thread about the ADC, I think something you could do is to sell the 2x barlow you’ve got now and get another one with a screw off lens cell, then you could screw it onto the nosepiece of the ADC and you can gain a lot of inwards focuser travel that way.

For example, the Baader Q 2.25x barlow is 2.25x natively and has a stated focal length of 44.5mm. 

The distance from the nose of the ADC to the top is about 84mm so putting the barlow cell on the nose should give you a barlow power of (44.5+84)/44.5 = 2.9x (roughly, this assumes your sensor will be level with the top of the ADC).

Just avoid Televue Barlows for this as although their lens cells screw off they do not have a standard m28 filter thread and so they won’t screw into anything else apart from their barlow body. 
 

 

 

Link to comment
Share on other sites

5 hours ago, CraigT82 said:

Hi Ross, I know your predicament from your other thread about the ADC, I think something you could do is to sell the 2x barlow you’ve got now and get another one with a screw off lens cell, then you could screw it onto the nosepiece of the ADC and you can gain a lot of inwards focuser travel that way.

For example, the Baader Q 2.25x barlow is 2.25x natively and has a stated focal length of 44.5mm. 

The distance from the nose of the ADC to the top is about 84mm so putting the barlow cell on the nose should give you a barlow power of (44.5+84)/44.5 = 2.9x (roughly, this assumes your sensor will be level with the top of the ADC).

Just avoid Televue Barlows for this as although their lens cells screw off they do not have a standard m28 filter thread and so they won’t screw into anything else apart from their barlow body. 
 

 

 

Cheer, Craig. Having a real headache over this one 😆  That seems like a good idea, though I’ve seen a couple of posts saying the ADC body itself is 30mm which would change the calculation a little. Either way, my best bet is probably to leave you folks alone and utilise FLO 30 day returns to see what works best! Thanks again.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.