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Oh, blimey....I've been Astrobooted

Moonshane

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Moonshane

Moonshane

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Someone linked to Astroboot last night and I made the mistake of following it. I have been thinking about replacing my school achromat (a 102mm f10) with a shorter faster achromat. One reason is that a wider field will be better for the kids to use and track down objects themselves. I am also on a knife-edge about getting a Lunt 50 or a Quark and I thought that a faster achromat might be better for the latter.

Anyway, I saw a 120mm f5 Skywatcher achromat at a decent price if it is ad described (i.e. new with a missing objective cap and dovetail bar). I have the latter and can easily make or get the former. So I went for it and will be testing it for white light views with a Lunt wedge later this week hopefully. 

I dallied between the 102mm f5 and the 120mm f5 but in the end felt the increased aperture will help in a number of applications and it still has a focal length of only 600mm, providing a potential maximum field of  2.7 degrees in 1.25" format and 4.3 degrees in 2" format with my existing eyepieces.

Looking forward to trying it out but either way, one of the two aforementioned will be kept and the other sold.

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John

John

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I keep a careful eye on that site. Some interesting stuff is on there from time to time and it's updated quite regularly too.

I've bought a few bits and pieces from there but no scopes, as yet.

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Moonshane

Moonshane

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I am not worried Nick as it does say 'performs best' which i take to mean 'may get hot when used with a scope bigger than 4"'. i will be using it for observing and sketching the sun for short at school sessions rather than imaging when i expect they get hot. with a 100mm frac it hardly even gets warm.

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nightfisher

nightfisher

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I got astrobooted yesterday, i ended up getting the skyhawk 114 f7.8 newt, god only knows why i bought it, i was only after a flexi slo mo, i think i will sell the newt on after having a play with it for a while, this is not the bird jones one but 900mm focal length, it was an expensive day as i also bought a black Burlesque  frilly dress  :embarrassed:  however i can assure you all that this was a gift for Claire, my partner, she has been hoping for one of these for a little while :cool: 

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spaceboy

spaceboy

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I am not worried Nick as it does say 'performs best' which i take to mean 'may get hot when used with a scope bigger than 4"'. i will be using it for observing and sketching the sun for short at school sessions rather than imaging when i expect they get hot. with a 100mm frac it hardly even gets warm.

May have some good news for you Shane.

As you suspected Lunt have recommended apertures due to the capabilities of the heat sink on the different size wedges. From what I gather your ST120 should be OK if you use a UV/IR rejection filter fitted to the front of the wedge in a similar way as Daystar recommend for diagonals when using the Quark over certain apertures.

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Moonshane

Moonshane

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cheers Nick

I thought it was dangerous to put filters before the wedge?

I found this which includes a reply from the designer of the Lunt wedge (Markus at APM)

https://groups.yahoo.com/neo/groups/Refractors/conversations/topics/32558

It suggests (based on the fact that he uses a 10" APO with a 1.25" wedge) that there's no realistic aperture limit or danger from using the 1.25" above 4", just that the unit may get a bit (or a lot) hotter. On the basis of what the designer says, I am even less worried now.

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spaceboy

spaceboy

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cheers Nick

I thought it was dangerous to put filters before the wedge?

I found this which includes a reply from the designer of the Lunt wedge (Markus at APM)

https://groups.yahoo.com/neo/groups/Refractors/conversations/topics/32558

It suggests (based on the fact that he uses a 10" APO with a 1.25" wedge) that there's no realistic aperture limit or danger from using the 1.25" above 4", just that the unit may get a bit (or a lot) hotter. On the basis of what the designer says, I am even less worried now.

Daystar state when using their Quark : For apertures between 80mm and 130mm you can use a Baader UV/IR cut filter in front of the diagonal.

As the lunt wedge works basically on the same principle of an unfiltered refractor objective upto 5" then I see no reason why it would be dangerous to use the same recommended UV/IR cut filter to keep the focused light to a safe level in the 1.25" wedge when using it with apertures above 4".

As for any reviews suggestion of a person using a lunt wedge of 1.25" or 2" in an unfiltered apo of 10" is frankly Ludicrous IMO. Even Daystar draw the line at a 5" refractor being used with the Quark :For apertures greater than 130mm a Daystar ERF should be used.

Personally as Lunt state recommendations on their website I would not exceed them simply because I don't want to risk anything when my eyes are involved especially where I wouldn't have a leg to stand on if something was to go wrong. Despite this I should think if a UV filter is absorbing the excessive UV light created by a larger aperture then surely only 1" of additional aperture shouldn't cause any major issue?????

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Moonshane

Moonshane

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I think the difference is actually in the design Nick. The wedge diverts 95% of the heat/light (all wavelengths) to a route outside the light path (which is then diluted further by a factor of 1000 by the ND3.0). Based on this there is virtually no heat, or UV or IR coming up the eyepiece (or no more than if you were e.g. birdwatching with bins or a scope on a sunny day) which is completely different to a quark where it all is but is then filtered out by whatever internal means the quark uses.

I share your views about eye protection naturally, but the designer of the Lunt wedge knows a lot more about the safe use of these units than I ever will and if he says that it's OK then I believe him.

There is no difference in the designs of the 1.25" and the 2" Lunt wedges, the 2" just has a bigger heat sink which keeps temperatures down a little. The type and quantities of light coming through a given aperture are the same no matter what the size of the wedge. It does not say the 1.25" wedge is unsafe for larger apertures, just 'performs best'.

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Stu

Stu

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My usual boredom got me thinking. Would it be possible to use say the 2" version of the lunt wedge in a large refractor 130mm + and plug the quark into that doing away with the need of an expensive ERF ??

This is answered in the Quark instructions Nick, and the answer is no. The Wedge removes too much of the visible light so would leave the Ha image too dark. All you need to do is block the UV and IR and leave all the white light.

3466c6c4a47a1c049b37c2e9917fee9f.jpg

The manual is available for download here:

http://www.daystarfilters.com/downloads/QuarkManual.pdf

Nick, I and a number of others have used 120mm scopes with UV/IR cut filters and the Quark and there really are no problems with heat. I'm sure you would find this combination very good.

One thing which may help is to position the UV/IR cut filter where use of its area is maximised without vignetting the image. This could potentially be achieved with extension tubes ahead of the diagonal and making sure it reached an optimum position in the light cone. Probably minimal improvement but some maybe.

Stu

Sent from my iPhone using Tapatalk

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spaceboy

spaceboy

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I am aware that some imagers have removed the ND3 filter from wedges to allow for better control over the light in the camera. If the ND3 filter is removed would this enable use of the quark ?? I'm obviously asking hypothetically as I won't be taking my wedge apart anytime soon but just wondered if it would offer an alternative to an ERF.

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Stu

Stu

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I don't know the answer to that Nick, but I suspect the answer is that it would not work still.

A UV/IR cut filter rejects virtually all or this energy and hear, and allows through virtually all the white light. An ERF is pretty much just a big UV/IR filter.

A wedge with ND3.0 removed would allow through 5% of the white light and 5% of the UV/IR. The Quark is designed to work with 100% of the white light so I'm sure the image would be very dim, plus you are still letting some UV/IR through

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hunterknox

hunterknox

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Has anyone used a Quark with something with such a fast f-ratio? I would have thought that would be an additional factor given that it dictates the intensity of the light/heat.

Shane: I wouldn't worry too much but maybe experiment with stopping down the 120 before going to full aperture.

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