Lunt 1.25 White Light Herschell Wedge prism

[Stargazer_00]

Hi all,

I currently have an ST80 which I use with a full apeture solar film and a baader solar continuum filter (pictures attached for anyone looking for what to expect from this product setup - photo taken with a smartphone 8mp camera - there is more detail really than these pics show but not loads more)

The views are ok I guess, considering what I paid. I can see some granulation near the limb, and can make out clearly the sunspots. Lovely.

I would like to be able to view the prominences and see more granulation on the sun and as such I did some research. First I read about HA filters and then found another article which suggested that a herschell wedge is undoubtably the best filter for viewing the sun in detail. Possibly with a polarisation filter for brightness adjustment.

the product I now have my eye on and want some advive on is:

http://www.365astron...ter-p-3045.html

[Stargazer_00]

I forgot my questions (lol)

Does anyone have experience of this type of filter?

Is it worth the (reasonably affordable) price?

Are the optics on the scope sufficiently good to bother buying this?

Thanks

EDIT: also realised that there is now an edit button... was that always there?

[Zakalwe]

To see proms you would need a hydrogen alpha filter (which are very expensive). A PST might be a good choice....you might pick up a 2nd hand one for £300-400?

The Herschel wedge will only allow you to view in white-light.

[Zakalwe]

Work on your focus with the kit that you already have too. This will improve your results too.

The image in your original post looks like the focus is a bit soft.

[Stargazer_00]

i think the picture doesnt do it justice to be fair. its a smart phone held up to the eyepiece. never going to get a good picture that way. I could see clear granulation on the limb and there were a lot of small sunspots that dont even show up on this picture. The view is ok. I just want to see proms.

I read an article that said you could see proms with a herschell wedge, is that not the case?

Also, for HA filter, is this something that screws into the EPs like the baader solar continuum filter? or something else.

the focuser on the ST80 is a little wanting as well. It does the job I guess but it is low end quality. I may save up for an ED 80.

[David Smith]

As said above, to see prominences you will need an H alpha scope. The wedge will not show you this.

[Zakalwe]

Also, for HA filter, is this something that screws into the EPs like the baader solar continuum filter? or something else.

You can get Etalons that fit onto the front. A 60mm one costs (with blocking filter) upwards of £2000. A 35mm PST costs about £500 new.

[RikM]

The wedge is good. Much better than glass filters but not exponentially better than Baader film. If you tweak the little grubscrews on the ST80 focuser they can be made to work properly. You won't see much more with an ED80 than your ST80 shows in white light. Of course there are other things you can look at where the ED80 would be be much better.

As said above, take your time over the focus, or perhaps try a webcam if you want to capture solar images. This was shot with an ST80, baader film and solar continuum filter.

[Zakalwe]

Baader solar film on an ED80, with a Microsoft Lifecam.

[Stargazer_00]

The wedge is good. Much better than glass filters but not exponentially better than Baader film. If you tweak the little grubscrews on the ST80 focuser they can be made to work properly. You won't see much more with an ED80 than your ST80 shows in white light. Of course there are other things you can look at where the ED80 would be be much better.

As said above, take your time over the focus, or perhaps try a webcam if you want to capture solar images. This was shot with an ST80, baader film and solar continuum filter.

This is approximately the same level of detail I can see visually, however in green. Did you use a graphic program (ala photoshop) to shift the light to yellow?

I like the idea that the prism mitigates the need for the full aperture filter. Im permantely paranoid that its got a tiny pin [removed word] in it i cant see and im going to blind myself. I like the idea that simply putting the prism in the scope means I dont have to worry, all the satefy features are built in...but at £180 I might as well just save and buy a 40mm PST?

I might try a web cam option, is there something relatively affordable I can use with the ST80? I havent tried any webcam imaging whatsoever. I assume it needs direct cable connection to a nearby laptop? I dont have a tracking mount, or even a mount with slow mo controls! Its just a pan and tilt camera head so maybe thats a bit pointless unless it takes still to be stacked later.

For the grub screws on the focuser, should these just be loosened ever so slightly to give the focuser a little more glide?

thanks for all your help, very nice the ED80 shot does show lovely granulation across the surface whereas my ST80 I can only see this around the edges.. possibly more a limitation of my eye than the scope.

[ollypenrice]

It is absolute nonsense to claim that you can see proms in a Hershel Wedge, I'm afraid. You can't. They give a superb white light view of sunspots and plages plus a little granulation. As the others have said, it is better than a front filter but not by an order of magnitude.

I'd save for a dedicated Ha scope which really will show proms and CME's etc.

Olly

[Zakalwe]

thanks for all your help, very nice the ED80 shot does show lovely granulation across the surface whereas my ST80 I can only see this around the edges.. possibly more a limitation of my eye than the scope.

The main advantage of the ED80 is that it is an APO, so will give less chromatic aberration than a scope like the ST80. The other difference is that the ST80 is f5 whereas the ED80 is f7.5.

The better chromatic control won't make that much (if any) difference when solar imaging. The f7.5 will give a smaller field of view, but it won't be that different.

I'd wager that you won't see that much difference between the two (I'm happy to be corrected on this). I still reckon that more careful work on focusing will make a difference. Focusing on the Sun can be quite tricky, so it needs careful attention.

[Stargazer_00]

Thanks for all the advice

I have seen a few thread on the internet about replacing the focuser part of the ST80 with an upgrade, possibly even a 10:1 focuser. Are there any UK companies that supply these?

Apprently GSO supply one but I can't see these on the net anywhere yet.

[Stargazer_00]

http://www.ebay.co.uk/itm/GSO-2-1-10-Linear-Bearing-Refractor-Crayford-Focuser-with-86-4mm-Base-Adapter-/110957442591?pt=LH_DefaultDomain_0&hash=item19d594361f

[Zakalwe]

Without wishing to sound unkind, buying a new focuser will probably cost more than your scope.

What is the diameter of the tube? I'm sure that there is something out there that will suffice.

[RikM]

There is no need to replace the focuser. I actually tightened mine up because there was quite a bit of play in it and image shift when focusing. I tightened and evened out the tension on the four big screws under the focusser and then tightened up the grubscrews on top a little bit to take the play out of it. It is now quite stiff to turn, but there is no image shift and the action is quite smooth.

Oh, yes...I captured the image in mono and added the colour in Photoshop. I actually did this with a QHY5 guide camera but I have also used a Phillips SPC webcam with more or less the same result. Sometimes I use it on an EQ3-2 with motors and sometimes on a static camera tripod. If you start the shoot with the sun close to the leading edge of the frame and let it track across as you capture the video then either Registax or Autostakkaert will still combine it into one good image for you. I can get about 40 sec avis on the static tripod using the QHY5 I think.

[Stargazer_00]

Without wishing to sound unkind, buying a new focuser will probably cost more than your scope.

What is the diameter of the tube? I'm sure that there is something out there that will suffice.

No problem I bought the ST80 as a fun little punt. It was just to allow me to have something I can take on my travels, set up easily on partially cloudy nights for spotting between the clouds, and as a way of viewing the sun.

For everything I consider more serious astronomy I use my Dob.

I dont mind the cost so much, I like the little scope and I think it'd work quite nicely with a 10:1 focuser. In reality my only actual concern is if it would still fit inside the travel case I bought for it.. shows you where my mind is at.

I believe the diamter of the tube is 86mm (from the listing posted above).

There is no need to replace the focuser. I actually tightened mine up because there was quite a bit of play in it and image shift when focusing. I tightened and evened out the tension on the four big screws under the focusser and then tightened up the grubscrews on top a little bit to take the play out of it. It is now quite stiff to turn, but there is no image shift and the action is quite smooth.

I'll try this first before spending any money Thanks for the tip!

[Zakalwe]

TS do one that comes with an adapter to fit it to an 86mm tube:

http://www.teleskop-express.de/shop/product_info.php/language/en/info/p775_2--Crayford-refractor-focuser---1-10-micro-transmission.html

£120 + shipping

Bern at Modern Astronomy has the TS Monorail (looks the same a the one in your eBay link) . It's £169 so a bit more expensive. They're supposed to be very good focusers though

http://www.modernastronomy.com/accessories.html#accFocusers

[Stargazer_00]

Excellent, thanks.

[Stargazer_00]

Can't edit the above now.. I just noticed that the above replacement focusers dont specify a footing for a finderscope. how do you get around mounting the finderscope if the focuser assembly doesnt have a place for it?

thanks

[John Wilkinson]

Suggest you buy a copy of the Springer book, "New Eyes on the Sun". It contains info for each type of solar observation as well as a lot of other info on the Sun.

[sologuitarist61]

I use a Lunt Herschel wedge for all my white light solar imaging as I am have two refractors and want to be able to use either and the Lunt enables me to do that. As the scopes have different apertures it would have cost me £80'ish for Baader film filters, so I thought the £140 I paid for it was worth it as the Baader film filters seem a little on the fragile side to me.