TheSkySearchers

I was looking for a 1.8x barlow but there are none. So started at a lower power with the 1.25" Nikon 1.6x barlow. Using spacer rings on the eyepiece barrel to move the eyepiece away from the barlow lens will increase magnification.
Using the micro guide eyepiece, the center linear scale, found 2 stars near Mars that were fairly bright, 7-8 magnitude, that were 20 units apart. Insert the barlow and the stars are now 34 units separation. Divide 20 into 34 and you get 1.7x actual for the Nikon barlow.
I was doing this to get higher power on a zoom eyepiece. Wanted the highest power to be 2.8mm focal length. So will get this with the .5" ext. ring on the eyepiece using the Nikon barlow.

You can get a micro guide eyepiece direct from China on ebay for $29.95. Search 12mm telescope eyepiece to find ad.
Agena Astro has the filter threaded 1.25" ext. tubes under their brand Blue Fireball. Fit and finish are really nice.

Hi Jones. A very interesting and informative post from you. Here is another tip on increasing a Barlow lens power for those who use telescopes with diagonals (refractors and catadioptrics) and may also call for the use extension tubes. Thanks for your post Jones, and the best of regards.

Jones wrote: ↑Wed Nov 18, 2020 6:12 pm I was looking for a 1.8x barlow but there are none.

There is a 1.8x 1.25" but expect to pay 375€ or more for it on the used market if you can find one. (TMB)

There is also the Kson 1.8x 1.25" which is a general use quality barlow
https://ensoptical.co.uk/index.php?rout ... ct_id=2723

Nice trick, thanks for sharing!

I have a Televue 1.8x Barlow (also a 2.5x, both are from the nineties). A few years back I bought two new TV Barlows, 2x and 3x , so now I have four. They're all 1.25". I bought the new ones because they were supposed to be better. I can't decide if that is really the case.

I've stopped buying Barlows.

The 1.8x is a rather long Barlow. I would really like it if it were worth €375! For that money I would gladly part with it!

I was just going to mention the TeleVue but they have not been available for a while now either.
I am not sure how hard they are to locate on the used market.

For a mild power increase with a 2" size, the Antares 1.6x is an excellent one.
If looking for one get the version without the twist lock though. The twist lock changes the parameters a bit and it is noticeable in use.

The true magnification factor of a barlow is dependent upon the distance between the focal plane of the eyepiece and the lens group in the barlow. I very rarely utilize a barlow in its 2x configuration. In the odd times when I might use a barlow it is typically only to unscrew the lens cell from the bottom of a barlow and screw it into the bottom of an eyepiece to give me a 1.5x factor. Truth be told my use of a barlow in any configuration is quite rare, as I prefer to use an eyepiece alone to increase magnification. That is simply my personal choice however, and not a statement on barlows in general.

Also have a 23-7.7mm zoom and a Baader Hyperion 2.25x barlow. It has a taller t2 to 1.25" clamp than a click lock. Looking at the double- double in Lyra with the 12mm guide eyepiece measured 12 units between the 2 stars. With the barlow added it is 32 units.
32÷ 12= 2.66x. Want to get 3x from the Barlow to get planetary powers from the zoom. A 10mm t2 ring gives barely more at 2.8x.
Put in a 30mm ring and got 3.16x a little too much..
Stacked up rings for 25mm and got right where I wanted at 3.0x.

You can get an assortment of rings direct from China on ebay. They have lots of t2 accessories to choose.

Nice trick, thanks for the share.

Using my 90mm f6.7 apo and double double again put the Nikon 1.6x barlow in normal position after diagonal and measured power of 1.66x. Then put barlow in front of diagonal and measured 2.5x. Used Baader prism regular t2 size. So that old wives tale of your barlow being 1x more in front of diagonal is true.

What formula did you use?
It rarely works out to be 1x in front of a diagonal.

Measuring the two stars distance apart. With no barlow they were 6 units apart, barlow after 90 they measured 10 units. 10÷6=1.66x.
Put barlow in front of diagonal 15 units apart 15÷6=2.5x using the micro guide eyepiece 12mm.

Here is another way to figure it out as well with an example if others want to figure it out.

Here is the formula to solve: 1+(D/FL)=M

To get those numbers we reverse the equation:
D/(M-1)=FL

D – Distance from top of barlow housing (shoulder) to center of elements
M – Barlow Magnification
FL – Focal Length

So my Antares 2x barlow is 68mm or: 68/ (2-1)= 68

Because it is going in front of the diagonal you must now include the lightpath length of the diagonal.
In my case it is 112mm:

112+68= 180

Now we use the first equation 1+ (D/FL)=M or 1+(180/68)= 3.64x