I read the reactivated post on comparing scopes and also read that there is a 33" MVA scope for sell. (Very good price, BTW). 
What is the advantage of a longer scope, say 33" or 36" over a 23" or 28" scope of the same power?
Never having looked thru the longer scopes (I do have several Lymans, Unertls and a DZ), I would think that the target would not be as bright with a longer scope as with the shorter ones considering the objective lens are the same size.  I do realize that the farther apart the mounts are the finer the movements would be.  Inquiring mind wants to know.

George

Mostly period Cool factor.  I thought I wanted a full-length one myself, but Jim Gier of MVA pointed out that it might not be possible to make adjustments for long range with a scope that long.  Also, the tube extending to the end of the barrel would mean having to clean the smoke deposits off the lens.

I still wanted one, and I still do.  But I went with the 28" version.  The spacing of the blocks on that length allows one MOA per division on the elevation adjustment, and the Cool factor is still Moderate-to-Severe.  I did notice at the Quigley this year that I was pretty close to the top of the elevation on the 805-yard Buffalo.  I doubt I'll be able to get to 1000 yards without a special height rear block.

A friend has the shorter MVA scope; I think it's the 23".  As far as I can determine, the optics and clarity are the same.  They are all six power, which is the maximum allowed for BPCR competition.

Full marks to Jim for his wise counsel.  He really wants his customers happy; MVA is a great company.

If the scope is long enough to use bases that drift into the existing dovetails, you don't have to drill a bunch of extra holes in the barrel (and ruin factory marks if that's where you need to position a screw mounted rear base), and the rifle can remain in factory condition if you later remove the scope. 
Many long scopes have the same optical working length of a shorter scope, and have a simple dust lens installed at the front of the tube ahead of the actual objective lens.
That way you can just cut a scope body length to suit various different barrel lengths without redesigning the  optics system.
The brightness of the light reflected off the target (some 200 yards distant) to the front of your scope isn't going to change much if the front of your scope is 6" or 12" closer to that target. 
Yes, you do obtain finer adjustments as the distance between bases increases, but you also use up more of the total available range of adjustment built into the mounts faster as well.
There are always tradeoffs.

My Seth Millard slug gun sports a very long Parsons scope. Using what fits. 

         Joe.

There is no power limitation for scopes in BPCR competition.   

Glenn you are right about the odd spacing on the 23" scope.  You have to be careful so you don't make a mistake.   There is a positive side to it though.  Less elevation to reach the longer ranges which keeps your cheek a bit closer to the stock.   I haven't used my 23" scopes past 500m, but they have piles of elevation left so would have no trouble at 1000 yards.

There are a number of people switching out the rear mounts for the DZ Arms ones.  I think that's a good idea.  No backlash and easy to read.

Chris.

Hmmm.  I think the reason that the old scopes were always so long had to do with the lens-making process.  Long focal length lenses are easier to grind and polish accurately, or were in the 19th century.  Also long F/L lenses don't have nearly as much chromatic aberration.   That's what I retain from my limited foray into mirror-grinding for telescopes, back in the '70s.  Of course the wider spacing between mounts has a positive effect.

uscra112 wrote on Jul 31^st, 2015 at 1:42pm:

Good points.
The longer tube gives you more wiggle room to make optic component position adjustments when the grinds of the lenses didn't/don't come out to spec, and the focal points have some variations from the designed specs.

While not a long scope, back when WRA was still making the A5, Winchester published a chart for their No. 2 and No. 1 mounts with the values for each "point" of adjustment at different ranges.
The No. 2 mount was shown with values using a 7 3/16" base spacing (only 0.0125" closer than the 7.2000" spacing later adopted by Lyman and others) listed from 50 feet to 1000 yards, and also using a 6" spacing with values for the same range of distances.
The No. 1 mount was shown using the 7 3/16" spacing with values from 50 feet to 200 yards.
Base spacing, TPI used on adjustment screws, graduation marks spacing, etc all interact for POI shift.

Not knocking their scopes and mounts, but MVA's 10.34" base spacing just doesn't match up with any of the pre-existing base mounting screw holes I have available, and since I won't "swiss cheese" my barrels by drilling and tapping additional holes, I use something else.