Solar newbie :-) seeks tips for focussing a PST with DMK21AU616 _

[Sp@ce_d]

Well, whilst I'm not new to imaging as such I'm new to Solar so would appreciate some tips here to save me wasting time. I've just taken delivery of a nice DMK21AU6 Mono to go with my PST.

Now my first attempts between those pesky clouds yesterday to focus were a nightmare.. the suns too bright.. how do you find anything to focus on! I know the focal point is close on the PST so I've tried with and without the top half of the eyepiece holder attached. However all I'm seeing is a white disc blury edge & no detail.. is that right? Whats the solar equivalent of a Bahtinov?.. boy we're so lucky in the DSO camp!

Any help on the setting for IC Capture would be welcome too.. I tried to turn down things but it's not really made any difference.

The problem is with the very limited testing time.. had 10 mins yesterday to catch the Sun between snow showers, there's nothing else you can test it out on is there?

Oh I should add.. I managed to focus enough to determine (blurry) sunspots with my SPC900 (with 1.25 nosepiece) last weekend with the top of the eyepiece holder removed so I know it can be done.. the DMK nosepiece & chip distance looks similar? I haven't measured it yet though.. I've a shorter one on it's way without the flange at the top.

[Merlin66]

The backfocus of the DMK cameras is 17.5mm - probably a bit more than the webcams...a barlow lens fitted to the end of the shoulderless nosepiece may help.

""" I've tried with and without the top half of the eyepiece holder attached""" Does this mean you separated the eyepiece holder and removed the section closest to the black box? This contains a "mini-erf" to reduce the energy loading on the final blocking filter (closest to the eyepiece)

Focus comes with practise...plenty of practise!

Get the solar edge in as good a focus as you can, readjust the tuning to get some surface detail and go from there....

[Ant]

I just got one of these to use with my dmk21 and PST and it works a treat.

http://www.firstlightoptics.com/adaptors/low-profile-125-nosepiece-c-threads.html

my tips.

1. Exposure times around 1/1250 (just a guide)

2. Make sure that the sun is in the field of view. This got me a few times as even the surrounding area is bright enough to trick you into thinking it's on the chip when it isn't

3. Then start focusing from one extreme and work your way through, you will at the right point see either surface details or if your lucky in your positioning the edge of the sun.

Then it's a case of fine tuning.

the PST has a little solar finder on the top, I've found on mine that the little "solar" dot doesn't need to be dead centre, but rather on mine slightly to one side, when it's in the right place it's significantly brighter.

Cheers

ant

[Sp@ce_d]

The backfocus of the DMK cameras is 17.5mm - probably a bit more than the webcams...a barlow lens fitted to the end of the shoulderless nosepiece may help.

I had a go with my TV 2.5x powermate.. result seemed to be the same

""" I've tried with and without the top half of the eyepiece holder attached""" Does this mean you separated the eyepiece holder and removed the section closest to the black box? This contains a "mini-erf" to reduce the energy loading on the final blocking filter (closest to the eyepiece)

No, the top part.. the holder itself.. I taped the nosepiece onto the top of the mini erf. Seemed to almost work with the webcam when I tried it.

Focus comes with practise...plenty of practise!

Get the solar edge in as good a focus as you can, readjust the tuning to get some surface detail and go from there....

Ha ha.. you're telling me it needs practice.. unfortunately the Sun's not out long enough in Scotland to get the practice I'm gonna need.

When you say Solar edge sharp, do you mean a smooth sharp defined edge?.. I can get that but can't seem to reveal any detail at all. Maybe I haven't got IC capture set right. I had a go at the daytime Moon with the cam after giving up with the PST. So at least I've got the exposure & settings working ok for that now.. it's actually a bit more sensitive to minor adjustments than I had thought.

I just got one of these to use with my dmk21 and PST and it works a treat.

http://www.firstligh...-c-threads.html

Yeah I wanted one but Martin reckons they'll be a little while before the next batch is made. I've got one in the post from Bern at MA

my tips.

1. Exposure times around 1/1250 (just a guide)

2. Make sure that the sun is in the field of view. This got me a few times as even the surrounding area is bright enough to trick you into thinking it's on the chip when it isn't

3. Then start focusing from one extreme and work your way through, you will at the right point see either surface details or if your lucky in your positioning the edge of the sun.

Then it's a case of fine tuning.

the PST has a little solar finder on the top, I've found on mine that the little "solar" dot doesn't need to be dead centre, but rather on mine slightly to one side, when it's in the right place it's significantly brighter.

Cheers

ant

Cool, ok I'll try that exposure setting. Yeah I can get it on the chip ok.. that finder is really neat. I guess I'm used to a slightly more refined feeling focusser.. it just feels like I'm winding in & out against a coarse spring. This is my backup plan for when we loose astronomical darkness up here so I need to get the hang of this. Although the other half isn't impressed realising I'll be at it in the daytime as well.. :shocked:

Anyway.. thanks for the help guys.. I'll report back in a month or so looking at the forecast..

[Merlin66]

Houston...we have a problem....

CAUTION!

The eyepiece holder on the current PST has two sections...The one which screws onto the black box has a "mini-erf" at the bottom, about 10mm diameter and "shiney"...the top section which holds the eyepiece (or camera nosepiece) has the smaller red coloured blocking filter.

BOTH these filters need to be retained in place for the PST to function. Without the blocking filter you will not get any effective tuning which shows the Ha features....

Can you confirm exactly which part(s) you were using.....

[Sp@ce_d]

Ah...oh dear .. I thought I'd seen somewhere someone doing this to get more in-focus travel. When I tried it without the holder it was the top section I removed with the block filter. All the energy reduction has happened before this hasn't it .

[Steep]

My pst must be an older version, I had to cut the eyepice holder down and did the same to a camera nosepiece to get the sensor to reach the focus point

[Freddie]

My PST is less than a year old and I can't focus my DMK21 even with that adaptor.

[riklaunim]

Use a weak Barlow lens. It just works (GSO/Revelation 2x 1,5" which has unscrewable lens cell)

[Ant]

A lot of my images (those not taken with the 2.5 tv barlow) was taken with the lens part of a cheapy SW barlow - you know the things that come with the scopes for free...

www.emberson.org

So I agree that you don't need anything flash for it to work.

Ant

[Peter Drew]

It is essential that you use the eyepiece holder with its red blocking filter as part of the system, without it you wont get a Ha image. Fortunately there is enough filtering before this position such that you should not have damaged anything.

[Sp@ce_d]

It is essential that you use the eyepiece holder with its red blocking filter as part of the system, without it you wont get a Ha image. Fortunately there is enough filtering before this position such that you should not have damaged anything.

Phew.. hope not.. would be a bit sickening to burn out a new camera

The short nose piece arrived today so it now fits in the holder right up to the body. Although I am now confused by the talk of barlows. I thought the problem was getting enough in-focus rather than back-focus?

[Merlin66]

Please, please...any members reading this post must be aware at all times the dangers of solar observing..

The Ha filters used in the PST (and other Ha set-ups) are very complex and usually have at least three elements (ERF, etalon, blocking filter) to achieve a safe and detailed Ha image.

Don't play around with any solar filters if you don't fully understand the risks - please!

[Merlin66]

A barlow placed in the nosepiece moves the effective focus further out and give a bit more distance to accommodate the 17.5mm backfocus of the DMK cameras....

[Sp@ce_d]

Please, please...any members reading this post must be aware at all times the dangers of solar observing..

The Ha filters used in the PST (and other Ha set-ups) are very complex and usually have at least three elements (ERF, etalon, blocking filter) to achieve a safe and detailed Ha image.

Don't play around with any solar filters if you don't fully understand the risks - please!

This is a very important point and I must admit I'm feeling a bit foolish about this now. I was under the impression the blocking filter only allowed the Ha part of the spectrum to pass and the energy had already been reduced to a safe level prior to this filter?

I certainly need to understand a lot more about this before I even think about venturing any further into the world of PST mods. Are there any good sources of information & reference you can point me to? I don't want to pick up any more bad habits like removing the eyepiece holder!

[Merlin66]

I have a write-up available on PST mods which also explains the construction of the PST and the Ha filters.

Drop me an email address for a copy.