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Stu

Burgess Optical 91mm Triplet - first light

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I say first light, it's actually second light but I had a better go this time although still fairly brief. The fine focusing was not working when I first got the scope, so I had a play around with that and successfully sorted it, plus made the overall movement better. Having bought a Moonlite for it, I actually think I'll stick with the original focuser, it does the job and is a fair bit lighter and less bulky, so more suitable for travel. When my numbers come up on the lottery I'll fit a FeatherTouch to it, but for now I'm happy.

The Burgess is an f6.6, 600mm focal length scope with a cemented triplet objective of fpl-53 and lanthanum glass. It has a removable section in the tube, perfect for binoviewing at native focal length, but also handy for travel as the tube splits apart.

The scope actually takes quite a while to reach ambient temperature. During cool down, the star shapes were pretty dodgy, looking a bit like pinched optics, but once cooled it looked fine. When I've finished my Harold Suiter book I'll make a more informed comment about the star test ?. Collimation looked fine though.

I was using the TAL alongside for comparison on the Giro-WR mount, with a 7mm BGO in the TAL and 3 to 6 Nagler Zoom in the Burgess to give roughly similar mags at around x140 to x150 but I mainly used the Burgess at 6mm ie x100.

There is some flaring around bright stars, perhaps just the objective needing a clean or muck somewhere else in the optical path so I'll check that out. Colour correction is excellent. No false colour on the moon and a nice neutral tone to the views. Side by side with the TAL, the differences are very noticeable, the TAL actually shows its larger aperture by way of a brighter image and slightly, but noticeably higher resolution on the moon and Jupiter, but also has a fair amount of false colour on the limb and on brighter stars. 

I didn't buy the Burgess as a planetary scope obviously, but it's nice to know that it gives enough detail on Jupiter to be of interest. Even while it was still low, there was detail in the two main belts and a couple of the temperate belts were visible in the polar regions. Interestingly though I didn't notice the GRS in either scope which should just have been visible towards the end of my session but to be fair I didn't spend long on Jupiter.

I am more interested in the widefield views, the main reason for getting this scope is to be able to take it south and view some of the wonderful objects in Sagitarius from dark sites. My lowest power eyepiece currently is the very nice 24mm Panoptic, nice and compact for travelling and giving a 2.72 degree fov. With a 31 Nagler it would be 4.24. The scope has a fairly flat field with the Panoptic, giving sharp stars across the fov. The field was definitely flatter than some of the faster ED doublets I've owned and the Pleiades looked lovely, as did the Double Cluster. Despite the bright moon, the DC was showing delightful tiny pin points of light with good colour variation in the red and orange stars.

Rigel's tiny secondary showed up clearly, although the flaring around the primary was more than I would have expected. Polaris split nicely.

On to M42, and although washed out by the moon, there was plenty of detail in the nebulosity even unfiltered, and the Trapezium was, well it was the Trapezium. Seeing wasn't brilliant but it looked sharp.

In summary, I'm very pleased with the scope. It is built like a tank, but is very compact still. With the focuser removed it fits nicely in my new 1510 Pelicase which is airline portable. I'll post a link to my contribution to the Grab and Go thread where there are pictures of the kit. The only negative really is that being a cemented triplet, I can't use it for solar without a front mounted D-ERF. I do have a 75mm one bought for a PST mod though, so perhaps I can source an adaptor to fit it on the dew shield and just accept the lost aperture.

More to follow when the moon is out of the way ?

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Sounds promising Stu although I don't like the sound of that flaring. Hope the cement between the elements is sound.

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25 minutes ago, John said:

Sounds promising Stu although I don't like the sound of that flaring. Hope the cement between the elements is sound.

Is that known to cause problems John? Not a lot I can do about it if it's the cement, it will just have to be a keeper!

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Haven't heard of the cement breaking down in these scopes before. From memory it was a type that never truly hardened, so they'd be some 'give' in temperature fluctuations. Standard optical cement that's used in small doublets, eyepieces etc, when 'breaking down' can look like a smear, oil streak or discolouration and most often starts from the edge. I've got a couple of old Tal ep's that are doing just that, but views don't seem to be effected.

As you've mentioned, I'd have a good look at the lens from various angles and lighting conditions, then have a look down the empty focuser draw-tube at a bright point source(moon, streetlight etc), looking for any reflective surfaces. I cured flaring on my 200K many years back, when I flocked/painted an overly shiny interior rear baffle tube.

This is highly doubtful, but always best to rule it out - See if the flaring occurs when viewing 'straight through', without the diagonal.

 

Andy.

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Many thanks Andy. I do hope it's something that can be solved because it is otherwise a nice little scope. On less bright objects the star shapes seem nice.

I was using a Zeiss Prism which I had just cleaned so I doubt that was the issue as it is fine in the Tak. I guess it's either the objective or something internal so I'll investigate more and report back.

My understanding about the cement is the same as yours, that it is not hardened, but more a very viscous fluid.

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Out of interest, what's the length of your scope, 'bare' ?

eg: My doublet is 580mm long, with lens cap on, dewshield retracted & with the std 10mm thick/deep 2"-1.25" ep adapter in place.

Cheers,

Andy

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