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Skywatcher pro 100mm or 120mm

durr

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durr

durr

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Hi to everybody, could anyone tell me which of these two scopes perform the best for planetary and moon photography and does anyone have any experience of the equinox variety? I have a HEQ5 PRO mount. Steve.

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Andrew*

Andrew*

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Hi Steve,

I'm not sure about this. I'm actually tempted to say the 100mm would be better for you. It's smaller, lighter, and it's much cheaper. It has the same focal length as the 120 so you would need to "push" (use barlows to multiply the focal length) it to the same extent to get a good image scale (size of the object on the chip). Also, the 120 is larger and faster. This might mean it's more prone to chromatic aberration, whereas the 100 is very well corrected in this regard.

Saying all that, though, the extra aperture in the 120 may mean you can push the image scale a bit more. However, I believe the 100 is very capable in this respect.

The HEQ5 will take the 100mm with ease. I've never seen the 120 but I imagine it's a bigger beast altogether and would be more comfortable on e.g. the EQ6 mount. Only a guess though.

I am not qualified to compare the pros to the equinox as I have no knowledge of the differences.

Please feel free to correct me guys...

Andrew

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durr

durr

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Hello Andrew thanks for your input I think I am leaning towards the 100mm refractor and will enquire about the equinox also. Whats the sky like up there is your site very dark? Steve.

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Viking

Viking

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Steve,

I understand that the Skywatcher Pro versions have the same optics as the Equinox. I think they are "true" APO at an "affordable" price. The main difference is that the Equinox models are supposed to have better mechanicals.

I have the 120 Equinox on an HEQ5 Skyscan mount. All I can say is that the views are outstanding. Suggest that you join a local astronomical sociey.

John

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Ajohn

Ajohn

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The 120 scope is sold with the eq5 so that's very unlikely to be a problem. Are you talking the equinox fluorite pro's or the evostar ed pro?

As the focal length is the same on both scopes the image scale will be the same so it isn't really correct to say that one is more suitable for planets than the other. The larger scope is more likely to have larger aberrations but it can be hard to say really one way or the other. F7.5 isn't going to stress eyepieces too much - that's a distinct advantage. It shouldn't stress the design of the objective either so that will come down to how well the lens is manufactured.

I looked at the ed pro but in the end went for a megrez 110. That's an F6 ed scope - no fluorite. That sort of technology may show very slight false colour at very high magnifications. Wish I'd had a clear night to see. Our of interest a usually reliable source tells me that this scope matches or outperforms the the zenithstar triplet that they used to make. This is most likely down to the use of better glass.

On secondary colour APO means that the scope will focus 3 colours to the same point. They usually meet off the 70% zone of the lens and don't from other parts of the lens. That's why it may be possible to see very slight amounts of false colour at high magnifications. There are also super apo's. Those do the same thing with 4 colours. The bottom line on all of this is that the performance of apo's varies. The 70% zone of the lens should give perfect images. The quality varies due to the lack of a perfect image from other areas of the lens. In the extreme the lens has to be recomputed according to the glass that is actually used to make it. There are also different quality grades of the same glass. So you see many scopes can be a proper apo but the quality can still vary. Don't let this put you off though.

John

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Andrew*

Andrew*

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The 120 scope is sold with the eq5 so that's very unlikely to be a problem.

Ah, but that doesn't really say much when you consider that the C11 is sold on a CG5 :(. Remember that he wants to use it for imaging. He will be restricted for additional gear (e.g. guidescope) with the 120mm with regard to mount capacity.

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MartinB

MartinB

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I have an ED120. It has excellent colour correction and lunar views show superb contrast. For any given eyepiece the size of the image will be the same between the 2 scopes however the extra aperture of the ED120 will give you better resolution. I have compared the ED120 side by side with a WO FLT 110 triplet and the small difference in aperture still allowed you to "see more" with the ED120.

I don't know the weight of the 120 but I was able to use is side by side with a ZS66 along with a load of imaging gear on a Vixen Great Polaris which is rated to 10kg. The HEQ5 has a bigger capacity the the GPDX so I can't see you having any problem.

The focuser on the ED120 is a Crayford and I like it but many people prefer the dual speed focuser on the equinox. I believe the focuser on the equinox is also rotatable and the draw tube has a compression ring. Whether you feel these things are worth the money is down to personal preference.

The ED100 is very hightly regarded and is a fraction of the price of the ED120 but then it is a much harder task to create a 120mm apo than a 100mm one.

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MartinB

MartinB

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It's a good point about cooling time Rus. The thing that Ade didn't like about the ED120 compared with the ED100 was the much longer cooling time. Not so much of a problem if kept at outside temp but a big issue if it's indoors and you want to grab a quick view of the terminator in between clouds.

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durr

durr

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hey guys thanks for the time and effort with your replies. I am now leaning towards the 120 mm pro series. I have a HEQ5 PRO mount so that should not be a problem with any weight issues. Now just a problem of who to buy the scope from, when I get this beast I will write a report on what Ifind and how I think the telescope peforms.

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Ajohn

Ajohn

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I'm still curious as to if we are talking about the fluorite or ed apo?

I would go for the 120 too but bought a meg rez mainly because I want it for imaging (F6, field flattener etc) and from experience of skywatcher quality problems. It's curious just how many of there achro refractors can be improved by making small adjustments to the lens cell.

Personally I would buy it of some one who has a reasonable returns policy. I did return a scope to SCS astro once without much trouble. He did appreciate the nature of the problem though and stopped selling that range of scopes. It was a russian mac newt and clearly hadn't been collimated. In fact collimated had clearly never ever even been attempted. The reply from apm was - look at info on cloudy nights - if only it was that simple. Both the spacing and the alignment of the mirror and lens on those scopes is crucial.

John

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Whippy

Whippy

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John, my understanding is that no-one is producing any more 'real' flourite glass due to both the financial and environmental costs it incurs. Most scope manufacturers now refer to Ohara FPL53 glass as Flourite.

Tony..

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durr

durr

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The telescope that I am referring to is the sky watcher Evostar fluorite ED apochromatic refractor 120mm, which uses the two element multi coated air spaced objectives. The second element is made from the Japanese FPL-53 glass. Steve.

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Ajohn

Ajohn

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Hi Tony I think that takahashi and others of the same ilk still may do but it's artificially grown crystal and gets nigh on impossible above something like 4ins.

The FPL53 glass comes from O'hara which I understand is a US company. See http://www.oharacorp.com/. Can get confusing though as a few glass manufacturers do make glasses with the same name. There are usually very minor differences though - some times advantageous ones when glasses are combined. As far as I'm aware O'hara are by far the largest manufacturer of ed glasses. Many of the optical design packages now also list a Chinese glass manufacturer. Being a cynic I'm glad to note that their ed glasses are FK something or the other. They are definitely coming on in that area and shouldn't be dismissed. Much use is being made of them.

Out of interest the best refractor design I have ever seen by far uses a Schott (german ed) glass that is a bit expensive and another glass from a Japanese manufacturer. Schott also make a glass of the same name but the Japanese one has very very slightly different characteristics in blue light.

John

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John

John

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It's easy to get really hung up on the type of glass that is being used in the lenses but what really matters is how accurately the lenses are figured, polished, matched and multi-coated. I've no idea what type of glass my Vixen ED102SS refractor uses and Tele Vue don't publish what they use in their refractors but they don't have many problems in selling them !.

That said, I do think that Synta and William Optics have done astronomers a huge favour by making high performing refractors available at affordable prices. I have owned 3 ED80's and 1 ED100 and all were excellent performers and an absolute snip at the price. I have also owned a William Optics Megrez 90 which again was excellent and superbly engineered but optically no better than the Synta scopes IMHO.

John

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durr

durr

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Well my 120mm ED pro arrived on Friday so now just waiting for a break in the weather for a first light report if anyone would be interested. The telescope looks and feels very well made and will fit very nicely on my HEQ5 pro mount. Anyone know what type of eyepieces are included with the 120 they look very well made. The cooling time down does not present a problem to me, anyone who owns a 8" Schmidt-Cassegrain will know what I mean. The tube is much lighter than I thought and should not present any problems placing on the HEQ5. The true test of course will be on the stars.

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