Hi,

I have a LX-90 classic with a 3.3 focal reducer, meade zero shift autofocuser, diagonal, with a 26 mm eye piece.  When I put my 5X barlow in between the diagonal and 26 mm eye piece I can not see anything even though without it I can see fine.  Obviously I found no obstructions in the barlow.  I also tried taking out the diagonal and putting the barlow and 26mm eye piece directly into the autofocuser. 

1.  Can any one explain why I might be seeing this?

2.  Is there a way to calculate as you add attachments what effect it will have on whether the view capacity (not sure what the correct term is) is exceeded?

Thanks,

Hi, macombej

The barlow will shift your focus point quite a bit - you will have to turn the focus knob a lot of turns to find it. Plus, your magnification will be extreme - so center your target very carefully in the eyepiece before adding the barlow. Be aware that as you focus, the mirror may shift a little to, so expect to have to hunt around a bit to find your target again.

The 5x barlows are really designed for use with faster newts (F4-ish native focal ratio, brings them up to F20). With your native F10 LX-90, you are getting F50 (10,000mm focal length) which will require truly exceptional seeing conditions to use at all. Your 26mm will give you 384x magnification with the barlow, which is right at the maximum usable magnification for perfect conditions with this scope. I would recommend a 2x barlow as being more useful for your scope under normal (average) conditions.

You will find links to dozens of calculators here:
http://www.martindalecenter.com/Calculators3A_1_DaTel.html

And this one is a favorite for figuring out what will fit in your camera:
http://www.newastro.com/book_new/camera_app.php

HTH,

Chuck

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Chuck Reese
CDIP Certified: Nebula, Galaxy, Solar System, Stars & Clusters Imager
CDIP Mentor: Nebulae & Solar System Categories
For information on the Certified DSI Imager Program, see:
http://autostarsuite.net/forums/1427/ShowForum.aspx

Use the reducer for wide fields. Remove it and use a 2X Barlow (or a shorter focal length eyepiece) for more magnification. Using both puts you at cross purposes.

 

What are you trying to do? I will assume visual observing for the following recommendations.

 

For the Moon and Planets 100X to 250X magnification is all you need given atmospheric turbulence. For Planetary Nebula and Globular clusters same thing, 100X to 250X is about right. For other DSO’s, usually the wider the field of view the better so 35X to 50X gives a great view. For all of the above use lower magnifacation to find and center the object and then switch to the higher magnifications. 

Hope this helps.

JimT

Unless I'm missing the point here, I think the problem is the 3.3 Focal Reducer.  It is my understanding that this size reducer is not intended for  visual work.

I have one, but  I only use it with my CCD camera.

But then again, I could be dead-wrong...

 

Jim

akjudge wrote:

Unless I'm missing the point here, I think the problem is the 3.3 Focal Reducer.  It is my understanding that this size reducer is not intended for  visual work.

I have one, but  I only use it with my CCD camera.

But then again, I could be dead-wrong...

 

Jim

Nope, Jim that's correct.

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