Orion SkyView Pro 8 EQ Reflector Telescope

[cap603]

I have a lead on this older used 'scope for a decent price. It's an f4. Can anyone tell me anything about it?

Thanks in advance.

[russ]

Well, it's an F4.9 Newtonian rather than F4 and is basically identical to the Skywatcher Explorer 200P. The mount is the same as the Skywatcher EQ5 but looks a little nicer. The scope itself looks nicer in its gun metal grey rather than the older Skywatcher's in their naff blue metallic but that's just personal preference.

If it's a newer model it should come with the single speed crayford and thumb screw collimation adjusters.

Should be a nice scope if the price is right.

[cap603]

Thanks for the reply. Actually, it's 800mm with a 200mm mirror, so that's f4, correct? How do you believe it'll perform in comparison with a true f4.9?

[dweller25]

For an F/4 scope you need to consider ......

It's designed primarily for astrophotography.

You will have to be spot on with the collimation for best results.

Eyepieces will have to be very good quality.

[John]

Thanks for the reply. Actually, it's 800mm with a 200mm mirror, so that's f4, correct? How do you believe it'll perform in comparison with a true f4.9?

I'm wondering if it's a different manufacturers optical tube on an Orion SkyView Pro Mount. Is there branding on the scope tube as well as on the mount ?.

As dweller25 says at f/4 collimation will be critical and it will be rather tough on low cost eyepieces as well.

[russ]

Thanks for the reply. Actually, it's 800mm with a 200mm mirror, so that's f4, correct? How do you believe it'll perform in comparison with a true f4.9?

That's interesting as Orion only started offering an 8" f4 very recently, it's their imaging scope. I've searched and searched Google but can only find the scope i described, the 8" f4.9 (1000mm FL). Prior to last year Orion didn't have an 8" f4.

I would ask if you have a link but i'm guessing you want to keep it under your hat.

[cap603]

Yes, it bears"Orion" on both scope and mount.

[cap603]

Since everyone I've encountered on the forum has been so forthcoming, so will I. Here's the eBay link: Orion SkyView Pro 8 EQ Reflector Telescope w/Tripod - eBay (item 350334226373 end time Apr-04-10 18:00:55 PDT).

I suspect this is an older item being sold from an eBay "store" in Eastern Pennsylvania (I'm located near Pittsburgh at the western end of the state.) Steep shipping price. I'm quite suspicious of the condition, but they do say they will refund the cost if the buyer is unsatisfied.

[John]

Since everyone I've encountered on the forum has been so forthcoming, so will I. Here's the eBay link: Orion SkyView Pro 8 EQ Reflector Telescope w/Tripod - eBay (item 350334226373 end time Apr-04-10 18:00:55 PDT).

I suspect this is an older item being sold from an eBay "store" in Eastern Pennsylvania (I'm located near Pittsburgh at the western end of the state.) Steep shipping price. I'm quite suspicious of the condition, but they do say they will refund the cost if the buyer is unsatisfied.

It looks an interesting scope although I'd ask some questions about the condition of the mirrors before bidding - I could not see any pictures of the mirrors which might be telling you something.

It might be worth a shot if you could get it at a price that reflects the risks. As already said an F/4 newtonian is going to be very fussy about collimation and eyepieces.

I don't think you will have many rival bids from this forum - most members are based in the UK !.

[cap603]

Would you mind explaining why it's intended for astrophotography? Would it not lend itself to regular viewing?

Thanks

[cap603]

Already done. They claim the mirrors are "clean and good."

[Cornelius Varley]

If you scroll down to the bottom of the listing its states that the telescope is a 200/1000 (f4.9) but one of the photos of the telescope show it to be 200/800 (f4).

Peter

[ollypenrice]

Why intended for astrophotography? Imagers want 'fast' telescopes which enable them to get more signal in less time. This means shorter exposures making fewer demands on their tracking accuracy and on the weather's ability to stay decent! They are into a good signal to noise ratio. They also appreciate the wider field of view on their relatively small CCD chips. Slight loss of contrast is nothing for imagers to worry about but visual observers want a lot of it. In this regard a small central obstruction is good.

Olly

[cap603]

So, what you're saying is that although shorter focal length 'scopes gather more light (as in camera lenses), the secondary mirror is closer to the primary than in 'scopes with longer focal lengths. This being the case, they impinge more, or block more light, on the primary? Is that correct?

[ollypenrice]

Partly, I think. The light grasp of a lens is proportional to its aperture only. But if it has a short focal length it has a wider field and can find more bright things in that field to illuminate the camera detector or eye. That would be my understanding.

For the second part of your question, yes, the central obstruction of a reflector has to get bigger if it moves down the tube. This impinges not only on light grasp but, more importantly, on contrast. But for an elegant explanation of why that is I must call upon people more comptent in optics.

Olly

[Astro_Baby]

YOu might also want to check the mount. The rear part of the RA axis looks to have no fittings for a polarscope. I'd expect the back end of this to be much like an EQ5 with polarscope fittings at least. This mount looks completely empty at the rear end. It may have been a cut down version.

Its also got the older rack and pinion focuser - unusual I would have thought for an imaging scope. The tec spec definitely says F4 though on the side of the scope.

[Cornelius Varley]

It looks like the mount is missing its RA setting circles.

Peter

[ollypenrice]

I did a bit of homework on the effects of central obstruction on low level contrast. Here is a reasonably accessible word on the matter;

Telescope Performance Factors

Olly

[cap603]

Thanks much for the information and observations!

[cap603]

Thanks again to all for the advise. Based on what you told me, I decided to let it go.

The search continues.....

[cap603]

The eBay auction for the telescope in question just ended. It went for $435, which is far, far more than I believe it's worth. In addition, shipping will be $70, for a total of $505. I can have a new Orion 8" Dobsonian for $330, plus $35 for shipping.

[Astro_Baby]

People always lose their minds on ebay - you could buy the scope new in the US for about $600 and have a warranty, free shipping and know all would be well.

I see it all the time on ebay - take a look at this one Helios Explorer 150 Astronomical Telescope F1000mm on eBay (end time 04-Apr-10 14:59:01 BST) old Helios scope with the extra lens in the focuser to give it a long focal length. Will be a pig to collimate no doubt. Went for £205

You could buy a brand new 150 on the EQ3-2 mount AND have the more rigid tripod for £219 and not have any hassles, dealer support, free delivery etc etc.