[UncleVanya]

I have a number of older lenses that were designed with Full Frame 35mm Film in mind. I assume that the hoods for these are designed with that in mind as well. Additionally tulip and rectangular hoods are more compact and efficient than round one's which the older lenses tend to have. My question is how does one mathematically calculate the ideal hood for a given lens? Is there a way to take field of view data and element size and calculate the ideal size.

Alternatively is there a desire to put this data into practical use? Could we start a thread or get additional data added to the reviews section to allow people to post their test photos and tested combinations of filters that work well on the APS-C sensor size? As an example, the 85mm A* f/1.4 has a rather large diameter long hood - I wonder if a smaller diameter hood of similar length could be used? I wonder if there is a rectangular or tulip shaped hood that would be a good fit.

Another topic - are there any screw in adapters that allow the use of tulip shaped bayonet style hoods on lenses that don't have the bayonet fittings?

[stevebrot]

You will want to use a somewhat deeper hood with APS-C than what you used with 35mm film. As with 35mm film, the exact hood to use sometimes requires some trial and error. I use hoods intended for moderate telephoto on my fast 50s and hoods intended for normal lenses for use in the 28mm to 35mm focal length range.*

There is a thread somewhere on this site where there is a general discussion. As for mathematical calculation, Google may be your best reference. The traditional approach, even for film is:

• Use the manufacturer's hood, if available
• Deep enough to shade the full diameter of the front element for light outside of the lens FOV
• Shallow enough to avoid vignette

The depth of the front element is the wild card as you might imagine.

As for finding tulip hoods that are calculated for use with APS-C and will fit your lenses, good luck...


Steve

* Round metal screw-in from heavystar on eBay. They also accept pinch-type caps.

---------- Post added 11-12-14 at 02:07 PM ----------

https://www.pentaxforums.com/forums/62-do-yourself/268066-diy-lens-hoods-link.html

---------- Post added 11-12-14 at 02:11 PM ----------

Oh, and as an example that practicality rules...




Steve

---------- Post added 11-12-14 at 02:17 PM ----------

...and a link to Lloyd's Excel spreadsheet calculator:

https://www.pentaxforums.com/forums/attachments/pentax-slr-lens-discussion/46...d-hoodcalc-zip


Steve

[Lowell Goudge]

I have a number of older lenses that were designed with Full Frame 35mm Film in mind. I assume that the hoods for these are designed with that in mind as well. Additionally tulip and rectangular hoods are more compact and efficient than round one's which the older lenses tend to have. My question is how does one mathematically calculate the ideal hood for a given lens? Is there a way to take field of view data and element size and calculate the ideal size.

Alternatively is there a desire to put this data into practical use? Could we start a thread or get additional data added to the reviews section to allow people to post their test photos and tested combinations of filters that work well on the APS-C sensor size? As an example, the 85mm A* f/1.4 has a rather large diameter long hood - I wonder if a smaller diameter hood of similar length could be used? I wonder if there is a rectangular or tulip shaped hood that would be a good fit.

Another topic - are there any screw in adapters that allow the use of tulip shaped bayonet style hoods on lenses that don't have the bayonet fittings?

A long time ago I uploaded a zipped file called hoodcalc.zip. It contains a spreadsheet that allows the calculation of the optimum hood as a function of focal length, sensor size and hood diameter .

It can be modified, if you know some math to design tulip hoods as well,

It needs some slight insight to know how to best use it, including the depth the front element is set back from the edge of the filter ring, but otherwise it can do a good job for calculating round filters.

[pacerr]

Wrap a tube of dark paper around the lens in question, hold it in pace with a rubber band, and slide it back and forth to determine where vignetting starts. The length of the tube in front of the lens will give an approximation of the maximum useful hood length at a given focal length. No math required.

I'd note, however, that in my experience a hood equal in length to the diameter of the filter ring of a lens offers all of the PRACTICAL off-axis, contrast destroying, protection you need. Any extension beyond that offers very little, if any, additional effect and becomes so inconvenient as to be left in the bag or at home when most needed.

Also note that any hood used on a zoom lens is only efficient at the widest FL that doesn't vignette -- if you're happy with the tulip hood on an 18-250mm zoom you've already conceded that point. Carry hoods suitable for both ends of the focal length range of a zoom lens for optimum effect.

The beer can pictured above on a 300mm/f5.6 prime was about 80% longer than necessary and was only intended to illustrate the relatively narrow angle of view of lenses used on APS-C DSLRs.

Many of the cheap plastic hoods advertised on eBay screw into the filter ring -- just order for the approximate FL and filter size needed. Again, keep in mind that the hood will only be minimally effective at longer FLs on zoom lenses.

---

Last edited by pacerr; 11-12-2014 at 04:19 PM.

[wombat2go]

The 49mm plastic hood for Pentax -M lens labelled "SMC Pentax 1:2.8~4 100mm" does not vignette down to the -M 28mm lenses .
Shown here with the K-01 and the SMC Pentax -M 1:3.5 28mm

[UncleVanya]

Wow thanks folks / excellent info!

---------- Post added 11-13-14 at 12:41 AM ----------

A long time ago I uploaded a zipped file called hoodcalc.zip. It contains a spreadsheet that allows the calculation of the optimum hood as a function of focal length, sensor size and hood diameter .

It can be modified, if you know some math to design tulip hoods as well,

It needs some slight insight to know how to best use it, including the depth the front element is set back from the edge of the filter ring, but otherwise it can do a good job for calculating round filters.

Where would I get a copy?

---------- Post added 11-13-14 at 12:42 AM ----------

Bayonet adapters out there?

[mgvh]

Free printable lens hoods? Here you go!
Free printable cardboard lens hoods

[Lowell Goudge]

Wow thanks folks / excellent info!

---------- Post added 11-13-14 at 12:41 AM ----------



Where would I get a copy?

---------- Post added 11-13-14 at 12:42 AM ----------

Bayonet adapters out there?

Stevebot posted the link

[stevebrot]

Where would I get a copy?

...and a link to Lloyd's Excel spreadsheet calculator:

https://www.pentaxforums.com/forums/attachments/pentax-slr-lens-discussion/46...d-hoodcalc-zip


Steve