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outfocus requirements Brandon 12 vs TV Plossl 15

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#1 Ebbisham

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Posted 03 January 2014 - 10:12 PM

I am thinking of ordering a pair of 12mm eps to ad them to my existing TV plossl 15,20 and 25mm pairs.
Quite curious to try a pair of Brandons after all i read here.
Now i noticed that i usually have to move the focuser out when swapping orthos for TV plossl.
With the TV 15 plossl and a GPC 1.7 in my Maxbright Bino i am left with 20mm i can move the focuser further in. This should be enough for the Brandons?
Unfortnately i dont know anyone with Brandons to test for myself.

Eddgie also mentioned when he moved from a Maxbright to a Mark V he needed additional infocus. Was this more than the 2mm the light paths from the 2 binos would suggest?

#2 Eddgie

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Posted 03 January 2014 - 11:00 PM

The light path in the Maxbright is only 110mm, but the light path in the Mark V is 123mm.

The Mark V takes about 13mm more in travel than the Maxbright.


The 123mm figure I think includes the Baader Quick Connect Ring that is required for the Mark V.

The Maxbright does not require this part. It screws directly to the T2 threads on the T2 diagonals. The Maxbright can be fitted with this, and if so, it adds about 10mm to the light path.

As for the eyepieces, it is not common for the field stops to vary by much more than 10mm, though some eyepeices with Smyth lenses can have much different focus travel than standard eyepeices.

#3 Ebbisham

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Posted 04 January 2014 - 12:00 AM

Thanls Eddgie, i already use the quickchanger with my Maxbright so i should be ok if i want to move to a Mark V and get myself a pair of 12mm Brandons.

#4 Eddgie

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Posted 05 January 2014 - 09:30 AM

Well, you should be able to tell just using the field stop.

Measure the difference in the field stop positions with respect to the eyepeice shoulder. The difference in dispalcement from the shoulder will tell you the difference of in or out travel that will be required.

If the Plossl is 5mm below the shoulder and the Brandon is 3mm above, you need 8mm difference.

Aprox anyway. Not all eyepeices come to exact focus at the field stop, but if the field stop in both is very sharp, then this should work.






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