250 px and BST`s

[nightfisher]

will BST explorer eyepiece`s work in a f4.7 250mm dob, also wondering about orthoscopics in same dob, but i guess they will be fine?

Need to consider eyepieces before making a major equipment change

[alan potts]

One for John I think.

Alan

[JamesF]

Orthos should be fine -- mine are. Really not sure about the BSTs though.

James

[John]

One for John I think.

Alan

I've never used a BST Explorer I'm afraid so I can't comment. Orthos will be fine though as James says.

[alan potts]

Really, sorry about that John, I knew you had tried out the many ortho's in scopes. I think the BST 's are going to start to show signs of softness at that speed.

Alan

[steppenwolf]

I suspect that they will be similar to my Hyperions at that speed - a little soft at the edges but fine in the rally interesting bit that your eye falls to naturally!

[nightfisher]

Thanks for the replies so far, this is all up in the air at present, but would involve me parting with my mak and HEQ5 syntrek in favour of a 250 px dob and tracking platform, im really starting to fall out with EQ mounts

[russ.will]

My opinion on this one does seem to be at odds with the rest of the world, but....

I don't think you'd find them very good, but you could also do worse, or no better for considerably more. To illustrate, in my old Explorer 200p (there's a scope I wish I'd never sold) which was 1000mm F5 they were extraordinary value. The 25mm excepted, I found you were pretty much in the last 10% of the FOV before astigmatism became unbearable. Across the central 60% they were as clean and sharp as anything I'd looked through for double the money - I looked through a workmates Hyperions when considering an upgrade and it took me about a minute to decide the Baaders may just be touch hyped. Okay in his long frac, but at F5? No chance. Throw in the relaxing combination of decent eye relief, a nice big lens to view through and a very effective eyecup and the BSTs are an absolute no brainer.

Fast forward to to the 1500mm F4.9 300p Dob and they were pushed somewhat harder. The small reduction in focal ratio may have an impact (well, it can't have a positive one at any rate) but the extra illumination afforded at a given EP focal length also drew your eye to the astigmatism, which now seemed to occupy the more like the outer 20% of the FOV. I was warned in advance of jumping to the ES82s that the lack of astigmatism, would simply reveal the scope's coma, but 30mm ES82 aside, I've found this to either be a lot less of an issue, or simply an issue I'm less bothered by. Astigmatism seems to bug me.

In a 250px, you're trading the additional illumination of extra aperture for a notably shorter focal ratio, which I personally would suggest will find out the BSTs even quicker. But that is a very subjective judgement and one that I must reiterate, you're very unlikely to improve upon with any other 60 something degree EP at even close to the price. The Maxvisions are a current exception to that rule, but are also a somewhat transient proposition, if current stock levels/non-shipment tales are anything to go by....

Retrospectively, if I had to stick with the BSTs to enable the jump in aperture, I would still do it, as a number of the smaller, duller more distant fuzzies can't easily be seen, or detail rendered well, without the extra aperture. Further more, they frequently don't occupy much area outside of the central FOV, so unless you get tetchy about starfields sharp to the egde to complete the view, you may not even bothered. Tracking also obviates this worry to a degree as the subject stays central - Only the larger and brighter objects showing up the edge of field funnies as they can span the entire view.

Put it another way, if the bottom fell out of my financial world, I'd keep the big Dob and sell the ES82s, as I know I could still get enough enjoyment out of using the BSTs.

Mind you, with 82deg FOV EPs costing so little as a personal import from the US, I'd also be tempted to get a manual Dob and forgo the idea of the fracking platform, but I don't image.

A few musings there - Hope some of them help!

Russell